Why would you even be concerned about your weight at this point in time? To lose weight you'd have to cut calories, which can deny your baby the important nutrients that your body is naturally asking of you to feed him. Backaches and leg cramps happen. Tough it out for two months and things will go back to normal after a while.
I don't think it's a good idea to be cutting calories right now. I've put on weight (currently 5 months pg) but I just try and go for the healthy options and snacks when I can and just accept any weight gain as part and parcel of baby making!