I have been on Metformin for 3 weeks for PCOS, I am retaining tons water and gaining weight very bloated still?

I was at 110 5'8" 4 yrs. ago, started gaining though I ate healthy and worked out a lot. 40 lbs. later I find out I have PCOS, now am being treated and was told Metformin would help me get normal and lose some weight. 3 weeks into it, I'm up 4 lbs, which feels like 20 beacuse of major water retention. I am extremely bloated, so can only tolerate 750mg. daily because my stomache gets so upset and bloated. Help???