Trying to figure out when i actually got pregnant

Okay so this is kinda confusing and ive never posted before so bare with me please ! The middle of december through Christmas i was sleeping with a guy and he didnt pull out all the time. That being said we did that on christmas and my period was due around then also. He didnt pull out and i started bleeding right away. Only it didnt seem like a normal period. We broke things off the beginning of january and all of january i didnt have sex with anyone untill the 14th. Which was right after glow said i had ovulated. However i already noticed tenderness in my boobs and was waiting for my period to come around the 24th. My symptoms gradually increased and i took a test when i missed the period. I went for blood and they said my levals were really low and that i was only two or three weeks along which freaks me out that it coule be the other guys. Only i already thought i was pregnant ? Any insight to this because im having a hard time understanding exactly how all this works based on research. Do you think i got pregnant in december like i do?