Hi Chayes, I had a similar problem when contractions hit for me, about a week before I was scheduled for a C-section. I was super miserable and hardly ate due to the pain, nausea, diarrhea, etc... Also lost like 5 pounds that last week. What got me through was some leftover pain meds from surgery (oxycodone I think). I checked to make sure it was "safe" for pregnancy first. Also took zofran. I was able to keep some food down and somewhat function after that. Without it I was basically spending all day on the floor or in bed in pain :/
Definitely check with your Ob-Gyn since you still have several weeks to go! You don't want to be losing all that weight in your last month. Hopefully they find a solution to keep you functioning well.