Weird period

allie

My period came 3 days late. I’m usually very regular and consistent. I’m barley bleeding. It’s more than spotting but I’m not even filling a panty liner in a day & I usually fill about 2 or 3 tampons a day. I took 2 test, one was invalid and the other was negative. There are small clots so I doubt it’s implantation. Has anybody experienced anything like this or know what could be going on?