dark dark brown blood & pain **nasty pic**

i am on nexplanon for about two years and haven't had a period since november. today i got my "period" but it's started off REALLY dark brown. the cramps are excruciating and it's not enough to wear a tampon or anything, but throughout the day the color is slightly more red but clotty and snot like... should i be worried? im 21 btw.