Can stress, changes in weight, alterations in medication, or illness affect the menstrual cycle?

Hello doctor,

I am a 21-year-old female with a height of 5.6 feet. I stopped taking birth control pills a few months ago, and I have been experiencing normal and regular menstrual cycles every month. These cycles are typically very heavy for the first couple of days and accompanied by severe cramps, but I have grown accustomed to this. However, my last expected period did not arrive as usual. Instead, I experienced very weak cramps, tender breasts, and light pink discharge, but there was no actual period. I have taken six pregnancy tests, all of which have come back negative. Nevertheless, I continue to have pink discharge (although not enough to fill a pad or tampon) alternating with normal-colored discharge. I also still experience cramps and tender breasts, even though my period should have ended three days ago. What could this be?