Is it possible to be around 3 months pregnant and not know?

I thought that I was pregnant in April (the whole birth control/antibiotics things), I was feeling pregnancy symptoms like very sore breasts, darkening of the areola (I'm a redhead you can't see them.. and they are now very visible), back and head aches, and nausea. All of the HPT I took came out negative, so I went to the doctor for a blood test, just to make sure. She did the one that just tells your yes or no and it came out No. Then I got my period but it was very light. I let it pass from my mind; but the pregnancy symptoms never went away and even more have added.. I'm getting heartburn way to easy, getting very tired from my easy job, the nausea still hasn't gone away and I've noticed that my lower stomach is starting to stick out more (or at least I think so.. I'm prediabetic so my weight changes all the time)

I've had two periods since I had the blood test (one right after it and the one the month after) but they have been very light.. I can wear a regular tampon and it half full after 8 hours. I've continued to take my birth control because I don't if I'm pregnant or not..

I really just want to know if any one else has had this experienced and found out that they were pregnant?