R.A.
Trying different formulas can cause discomfort and gas if switched on/off fast. I would continue with the Similac sensitive until you can visit her Dr. Again. It could be she also has Reflux or allergy.
Don't feed too fast, and ensure you stop to burp often. Check to make sure the bottle isn't filled with air either, as this can cause same symptoms.
That's all the advice I know as I haven't had an infant in 10 years! Good luck sweetie.
The constipation can be an issue that will need to be addressed by Dr. I would call Office or nurse for advice on the constipation.