And the past two days she has been screaming her head off. It feels like she has teeth coming in on the right side but on the back. I've been told that babies don't cut the back teeth first is this true? What can I try to calm her down where she takes a nap, she hasn't really slept past two days either

Have you taken her to the doctor yet? Sometimes but not always, teeth coming in are accompanied by a low grade fever. She is very young to have those set of teeth coming in. It could be that her gums are just irritated. It is so hard to tell what is exactly wrong with a baby at that age. If you feel that she is in pain, take her in to see a doctor. It could be a load of stuff you aren't thinking of.

I have taken her to doctor and she seems to think its her formula making her fussy but she has changed her formula a lot here lately and baby does good for a few weeks and then starts being fussy again

Hmmm... I am not a physician by any means so this is just my opinion...

Maybe the formula is making her gassy. Have you tried the Mylicon drops? They did wonders with my son. He had a lot of problems with gas and reflux so my doctor put him on Carnation Good Start. That did wonders. Another problem it could be is Colic. Has the baby been having any digestive problems with spitting up or very loose or hard stool?

The doc put her on enfamil gentlease for baby's with fussiness and gas. We use the gas drops she hasn't had any digestive problems

My son had problems with different formulas and it turned out that he couldn't have regular formula they had to put him on soy formula and that helped a lot, this does not mean that they are lactose intolerant though, my son now drinks regular milk fine but couldn't handle it in the formula, I also used gas drops by little tummies and they worked great for him, good luck hope all goes well