Are these signs of a possible pregnancy?

I have been on the pill for the last 18 months (since the birth of my second child). This month I have been extremely busy and there were a few days that I took my pill 8-12 hours late. My husband and I had sex on day 12 of my cycle. The next day and the day after I noticed watery, stretchy cm and then it turned to thick and yellowish discharge. I am now 8 dpo and for the past 2 or 3 days I have been experiencing heaviness in my pelvic region, frequent urination, swollen breasts, visible blue veins on my breasts and pronounced white spots on my nipples and today I started having headaches. I took a test yesterday and the day before and both came back negative. I don't usually experience pms symptoms except headaches. Is it possible that I am pregnant even though I haven't really missed any pills but took some relatively late and got 2 negative HPT's at 6 dpo and 7 dpo with the symptoms I'm experiencing?? Serious answers only pls! :)