2 weeks late no protection negative tests still pregnant?

I am 19 years old and have had pretty steady periods since I was about 17. My cycle usually runs about 31 days. I am now at day 45. I have had no signs of a period either. There are no chances of std's as I am married to my first. I am his first as well. I have taken about 4hpt's and all negative. They are just the little strip ones you can buy online for like 0.45 or whatever it is. A couple days ago I started to get this light brown spotting and today it was a little pink. It wasn't like a period and only present when I wiped. My breasts are a little sore, I'm tired alot more than normal. My lower abdomen feels very tight and bloated. I usually don't have any bad PMS signs, and my periods are pretty heavy. This is a first for me and I don't want to call the doctor yet because, well, I'm scared. Either way I do not mind, I just need some advice. According to a tracker, I ovulated about May 5. I think we might have had sex around then, but I'm not positive. We use no protection, but we use the pull out method. He stops when he gets close, and finishes on his own. I am allergic to latex and lubricants irritate me. We have been pretty lucky I'd say. Is there any possibility that this could be plantation bleeding or whatever is it.