I don't remember much acne with my son, but when I got pregnant with my daughter (like you, right after I finally lost all but the last few pounds of baby weight from my son), it seemed like my face went into triple-overdrive on the oil production. Since I'm a Mary Kay consultant, I used the Combintation to Oily 3-in-1 cleanser & moisturizer, and spot-treated with the acne treatment gel. That combination really seemed to do the trick for me.
Naturally, you should try to get your water intake up, and the sode intake down, but at this point, even balancing it 1/2 & 1/2 ~ deciding that after one glass/can of soda you can't have more until you've drunk at least that much water as well.
I also had back problems with my daughter, and I would recommend a good heating pad. However, a word of caution, DON'T use it while sleeping & of course, only on your back, neck, shoulders, and NEVER on your belly.
Good luck with your pregnancy. I said a prayer for you & your family!