help???

okay here’s the story: i have a bad case of the flu, haven’t been able to barely eat for a week, and have lost a TON of weight. i had protected sex on the 21st, which was day 12 of my cycle. on day 15 of my cycle i started getting really light brown discharge. it has slowly gotten darker til it got to this point this morning (very dark brown with black clots)... any possible explanation? should i be worried? (ovulation bleeding? implantation bleeding? just the sickness messing up my cycle?)