How far along are we?

I had my last period on January 13th of this year; no period in February, but I was so busy taking care of my sister who just had a baby and then immediately my grandpa's health worsened and I helped care for him until he passed. I figured I had no period because I was rather stressed. I took a cheap pregnancy test somewhere around the first of this month, I would estimate - just a cheap Dollar Tree one. By the time my cycle should have rolled around this month I was feeling it: extremely tender breasts, tightness around my uterus, and increased cervical discharge. I tested again March 15th and got my positive test result!!I go to the doctor tomorrow, so I guess I'm curious what all of you think: did I skip my period due to stress in February, and thats why I had a negative result around the first of March? OR, did I get pregnant when I ovulated in January and I just used cheap tests/wasn't far enough along to show up on a test?