I'm a "fun size" Ftm ... Needing suggestions

I'm 25 weeks and all the horrors of pregnancy are finally starting. I've been one very lucky lady thus far, but within the last week pregnancy is finally starting to catch up to me. I'm 5" previously 120-125 lbs... I'm now at 137 lbs. I understand that gaining weight is good and invitiable, but I feel aweful, it's taking a toll on my body. My lower back hurts so badly I swear I'm going to slip a disc out of place. And my belly.. Whoa!! I'm so scared about getting bigger and I still have 3 months to go...