When to take a pregnancy test


So I'm not very sure about when I should take a pregnancy test. I'm new to all of this. We had sex Dec. 1 after my period ended and then a few days later I had irregular bleeding (I guess an irregular period) and it lasted from the 8-14. I have not missed my period yet technically because it should be here within 9 days if I base off from the irregular bleeding. But it should've came before Christmas based on the original. When do I take a test? I took one a few days ago (before Christmas) and it was negative but I thought there was a slight shadow of a line but it could've been an indent. I'm sorry for all the posts, I'm just really new to all of this.