I don't know about the splenda, but I think mercury can cause it. I used to have that kind of problem. I once had 3 periods in 6 weeks. Now I don't get any. They got less over the past ten years. My last one was 2 years ago. The doctors say I have PCOS (poly-cystic-ovarian-syndrome) even though I don't have the cysts (or didn't at last scan). I never went on birth control either.