First, congrats for breastfeeding your little guy w/ his food allergies - that's WONDERFUL, and such a healthy choice for BOTH of you.
Second, here are just a few things to consider:
1) As another mom already noted, the symptoms you mentioned actually sound a lot more like TEETHING to me than "solids readiness" -- here's a list of signs of developmental readiness that I think really "gets it right" in case you are open to considering that at 5 months he is likely not ready for solids, especially considering his history of food allergies:
http://www.kellymom.com/nutrition/solids/solids-when.html...
Additionally, babies w/ food allergies typically start solids LATER, almost like they have this instinctual self-protection mechanism. Plus, breastfed babies in general tend to start solids later than average. So try to trust that when your son is ready, he will simply be very obvious about grabbing food from your plates at mealtimes, eating it, and clearly looking for more. This is different from his wanting to play and experiment w/ food, which he might currently want to do and which is really normal as well.
2) Teething can also create green stool and temporary stomach upset. But, so can the fenugreek! So if you can determine his teething status and can really confidently say he is not teething, then I'd suspect the fenugreek. There are other options for galactagogues, both herbal (goat's rue, blessed thistle, etc.) and pharmaceutical (Reglan, Domperidone), and likely without soy (herbal tincture, not in capsule, for example). For help w/ galactagogues to increase your production that are free of dairy and soy, you can consult a local, respected lactation consultant (IBCLC).
3) As you're looking for here online, you can also connect with your local breastfeeding/parenting community to talk to other moms who have been through what you're currently going through -- that is, breastfeeding a baby w/ known food sensitivities and what things to consider w/ maintaining milk production and introducing solids. Here are just 2 places to look locally and in person, if that interests you:
http://www.lllohio.org/groups/columbus.html
http://www.columbusapvillage.com/
4) Pumping -- I'm assuming you're using a personal pump that you purchased or got as a hand-me-down from a friend/relative. There's a possibility that your pump is not optimally functioning, thus not removing the milk as thoroughly, thus causing your milk production to decrease. In order to increase your production, you can temporarily rent and use one of the hospital grade pumps like the Medela Symphony or Classic (more effective, better for production issues). Hospital grade pumps can be rented from lactation practices and some pharmacies and some hospitals (call your local LLL if you have trouble finding a rental location). You can also increase your # of pumpings while away from your son (ie., add 1 more than usual). And of course, your baby is the best milk-remover, so when you're with him, you can feed him on cue which should help your body to produce exactly what your son needs.
5) If starting solids still seems like your only option, simply be very systematic about how you go about it --> to maintain your milk production, ALWAYS nurse first and then offer solids, keeping a detailed food diary for the first 6 months where you record what he's eating and how his behavior and his body react (fussy? constipated? eczema? painful gas? baby acne?). Only introduce one single-ingredient whole food at a time - preferably that you make at home (even baby food purees often have more than 1 ingredient!). Good starting choices include bananas, avocados, sweet potato, poached chicken, etc. Most of those grain baby cereals are not so nutritious for breastfed babies, but they are an unfortunate cultural habit that still sticks around (rice cereal flakes, blecch, have you tasted that stuff?). Whole foods are your best bet, and you *always* know a sweet potato is dairy free, soy free, and preservative free! Can't say the same for cheerios or gerber finger puffs or wagon wheels, KWIM?
Hope some of these ideas have helped in some way -- and if any of the suggestions don't resonate with you, simply ignore them! :) And once again, please give yourself a HUGE pat on the back for breastfeeding and for being so aware of your baby's food sensitivities. Having been through it myself with my son (dairy and soy, too!), I know it takes dedication and effort to stick with the breastfeeding while eliminating the offending foods from mom's diet --> but I also wouldn't have it any other way and feel grateful that breastfeeding worked out (we're still going strong, and he's well over a year now).
Best of luck!