pregnant or not!?!?

Me and my SO had unprotected sex the 24 of dec. which is fine we already have a 3 year old. I usually start the first of the month sometimes the first sometimes the 5th. Well, I haven't started yet and I have been feeling sick to my stomach. I have took 3 pregnancy test all of them negative. I just started feeling sick this week. Idk what to do....😞. Did this happen to anyone? Found out later that you was pregnant or I am just going crazy.