Anyone had shorter period for no reason?

My period is usually regular and around 6-7 days. Normally, I bleed for two days then it becomes lighter (more like heavy spotting?) then very light spotting for the remaining days, sometimes disappearing for about a day in between. This time, I'm almost on my 7th day and no sign of anything since day 4. It started off a bit lighter than usual and very watery/stretchy (sorry if tmi) for two days then on day 3 and part of day 4 very very light brown spotting. It disappeared after that and I've been waiting for it to come back but there is no sign of it doing so. I took a pregnancy test today just in case and it was negative. It was on our 13th cycle TTC. Anyone had this happen for no reason? Too scared to do fertility testing.