Bleeding after sex...

I had a period from the 18th to the 22nd of December. I had sex Christmas eve and on Christmas Day. With no issues. Everything was fine. Then Yesterday on New Years eve I had sex and I noticed some blood afterwards I didn’t think much of it. I recently started having sex with someone new. After having sex with the same person from January to July of 2019. So this new sexual partner has a bigger.. yanno.. maybe that could be the reason. Does anyone have any idea what this is ? Or what could have caused it?