Hi, R..
Best of luck with this. I know how hard this is. When our 21-month-old son was about 9 days old, we went through something similar. We consulted with the pediatrician and switched him to a ready to feed formula. Yes, it is expensive, but it was better. Despite the fact all formulas have the same nutritional value, the consistency is what is different in the ready to feed versions versus powder. The RTF is easier to digest, too.
We were told we could try and switch him to powder whenever he was older --- tried, and it never worked. However, on the RTF, he did a million times better. So, we just kept him with it.
Also, when he was about two months old, I put about 2 tablespoons of cereal in his bottle (avent makes a nipple that has the ability to change the flow --- there are three lines on it - one is for slow flow, two is for faster flow and three is for fastest flow.) That way, I didn't have to "cut" any nipple. But, you might consult with the pediatrician before adding rice cereal to a bottle.
One more idea --- you might try switching the baby's bottle. I used the avent with our younger one, and he did good. I have also heard good things about the Dr. Brown's bottles.
Also, ask your pedi for formula samples. Most peds get a lot and are glad to share. Also, like another mom suggested, I wouldn't switch formulas -- find one and stick to it.
In addition, call the manufacturer of the baby formula and ask for more coupons. Most of the time, they'll give them to you. Also, they sometimes have people on call who can give you advice on what formulas to try, etc. Most of the folks are super nice and more than willing to help whenver they can.
Ultimately, I think you should consult with your pediatrician and get medical advice on this. Babies shouldn't have to hurt.
Good luck!