Radom bleeding?!

So I was supposed to get my period on 1st Dec but it ended up being a week late, haven't had unprotected sex but tested in case and it was negative. After that, my next period came on time (about 28 days later) and I'm due to start on 31st Jan for my next. But today I started bleeding at I think about 2pm, but I've only bled once and haven't bled again yet. It was heavier than id consider light spotting and was more red compared to a lighter pink that id normally start a period with. Any ideas what this could be?