Adipex messes up my cycle

I was on adipex for about 4 months with no changes to my cycle (regular 30 day cycle), and i lost 40 lbs. I took a break from it for 3 months & now I’m back on it. This time, my periods are 5 days early and very painful, but short. Anyone else have this same issue? Going to start OPKs this cycle to see if im ovulating with these 26 day cycles before I see my doctor about it. I’m aware this happens to a lot of women, just wondering if someone had a similar experience and can tell me theirs.