Hi, I too have had difficulty making enough breastmilk right from the beginning and have had to both pump and supplement formula to feed my baby. A couple of helpful things...
First, I have realized how much stress is a factor and although not making enough milk is inherently stressful, as much as you can get good rest, eat well and release all the build up pressure and anxiety the better! I know, hard to do!
I have found some support from various herbs...fenugreek capsules and a variety of supplements from wish garden herbs are supposed to help with both milk enrichment and supply. Have you talked to a La Leche League member or a lactation consultant? Some one on one time to help with your latch may be a good idea.
I also have been taking a prescription drug called Domperidone which you can get from many international pharmacies and although it is used to treat some intestinal disorder, it is also known to boost prolactin levels therefore increasing milk supply. I am not sure if it is working too well for me, but it may be worth looking into. Look up Dr. Jack Newman, he is a leading pediatrician on breastfeeding and his site has been helpful to me.
What formula have you been using? I have been feeding my baby girl Earth's Best Organic (whey) along with breastmilk. At first she experienced lots of gas and even constipation, though no vomiting. So I have added some baby probiotics which are good bacteria to help her digest the formula and also Gripe Water which is a liquid supplement to aid gas, indigestion, nausea and other symptoms. With these supplements, she has had few problems eating this combination and I have been able to not stress so much about producing less breastmilk than she needs!
Please let me know if you have other questions! I truly understand how hard it can be during this time!
Much love,
L. and Lila (4 months)