Hi Jenny,
I feel your pain! I'm definitely a worrier too. I had major anxiety and lost so much weight because of it. Don't worry, it will get better.
My daughter is now 12 weeks old and for the first 6 weeks of her life, we were going crazy as to what the reason was for her crying and cringing. I still think it was the breast milk. I was supplementing with Similac Advance with Iron also, but she was still arching her back and crying all the time (when she wasn't sleeping). I switched to Similac Advance Soy formula and she was still cranky. I was calling the pediatrician everyday and sometimes more than twice a day because I was going crazy!!! The doctor told me to switch to Nestle Good Start and we've been on that ever since. I stopped breastfeeding around the same time I switched to Good Start so I'm not sure if it was the switch or the stopping of breastfeeding that helped, but she is 98% better since then.
I know it's nerve racking, but try the switch to Good Start and give it a couple of days and see if it gets better. It's cheaper than Similac Advance at Wal-Mart. Right now Target has the special size (32.1 oz) for the price of the 25.7 oz.
Hope everything works out and you can email me personally if you have any specific questions. Good Luck!!!