pregnancy test help please

Is there any reason why a at home urine pregnancy test wouldn't detect my hcg level. 
I have been taking pregnancy tests every week since around 4 weeks after I had sex. I got my period but still didn't feel right so I continued testing. It's not like I'm early in pregnancy I would be in my second trimester by now and I still don't feel right. I have Continued to take pregnancy tests just incase but they have all been negative, not even a faint line! I take them at all different times of the day and some of them I even wee in a cup and then test.