Period Late Hcg level was 1 day I was suppose to start.?

Last month period was eight days late and only two days when it finally started. This month my period is four days late if it was supposed to come in 28 days. Not sure about that because that is my first irregular period. I usually have them every 28 days for 10 days. I was diagnosed with endometriosis. I was going to have a hysterectomy but we decided to TTC. I have all the same symptoms of my last pregnancy's but when I went to the doctors to have blood drawn it came up 1. Just curious when I could test again with a hpt and what are the chances that I am pregnant.