Homemade formula is a big undertaking; it can't be made more than a day ahead and you have to struggle with sanitation (ask your grandma).
I've heard that most homemade formulas you can find on the web don't have the right nutrition -- too much casein, not enough fat, are hard on the baby's kidneys, or are otherwise problematic for babies. I tried about a dozen different brands of commercial formula when my preemie baby needed a supplement because my breast milk had nearly dried up. I was extremely frustrated when the doctor finally listed for me which of the formula brands I had been using were detrimental to my baby's health.
Seeing a nutritionist was the key to finding a formula that my daughter would take and grow on. Only one store in the Seattle area carried it, and we finally ordered it direct online. My daughter also had a problem sucking thoroughly, which we got a therapist for (referred by the doctor). It's amazing what you can teach a baby that young.
There is nothing worse than being told you're not able to breatfeed your baby sufficiently and that she has "failure to thrive". Hang in there.