Sounds normal to me.
Tenderness of your boobs is a classic sign that you are due on.
Pregnancy soreness in boobs is somewhat diffrent, normally its your nipples that are sore and incredibly sensitive and your boobs feel fuller and heavier, possibly larger, but from what I have been told and from what I remember from when I was pregnant, my nipples hurt like crazy, could not wear loose clothing at al, ended up putting band-aids on them to stop them rubbing on things!
If you are late there are a number of things other than pregnancy that could put you out a few days.
Stress
change in eating habit
excessive weight gain/loss
excessive excersise
i started a new job 2 weeks ago and the stress from it knocked me back 6 days ... Had me woried I can telll you that!
And in answer to your question abotu dissapearing soreness...
It is possible, but a dissapearnace in sighs of pregnancy altho does nto always mean it, but can mean that the levels of hgc and pegesterone in yous system are dropping and you are loosing it.
But in all fairness.. If you had your peroid, boobs went back to normal, and then get sore before another peroid is due I say your pretty safe and not pregnant.
But to avoid posts like this in furture.. Please use protection, if not just to prevent pregnancy but to prevent you getting any stds. If yoru boy sleeps with you with out protection whos to say he hasnt in the past been with others with out protection.