T.H.
I just went through the same conflicting feelings. I have anxiety, have tried 5 different anti-depressants and counseling over the past 5 years. I've found that while counseling has given me great coping skills, I really feel much better when I'm on an SSRI. I stopped taking them before each of my pregnancies, and held off taking them while nursing until things got really bad before starting them back up.
My son was 6 months old when I decided to go back on paxil. I was worrying about everything to the point where I was spending more time with my anxiety than enjoying my kids. Both his pediatrician and my OB said there would be no ill effects, but it worried me that because paxil is such a new drug, there haven't been any long term studies on adults who were nursed by moms on SSRIs. I knew that if I was taking the drug and exclusively breastfeeding, I would be worried about the possibilities (and that would cancel out the effects of the anti-anxiety meds!) I decided to wean him, but keep one breast-feeding a day - that way he would still get the immune system benefits from breastmilk, but less Rx. He recently gave up that one early morning feeding, and is now exclusively formula fed (with solids, too).
Do I feel guilty that I'm not breastfeeding the whole first year? Absolutely. As soon as we weaned he got his first cold, which made me feel like a terrible mom. I think that you need to know yourself and trust your instincts. I know that I'm being a better mommy to my son now that I'm taking the meds. He needs ME - my comfort, my time, my energy - and will be perfectly healthy with formula. Your baby needs a happy mommy, and if the meds are working for you, I feel that need outweighs the nutritional benefits of breastfeeding.
Whichever decision you make, do not allow others to make you feel guilty. You need to do what YOU believe is best for your little one...you're a great mom for taking everything into consideration before you make your choice.
Best of luck!