Ok the only way you can possibly get pregnant is if any sperm (even pre-cum) from his penis has got into your vagina.
If that hasn't happened then you aren't pregnant, even more unlikely seeing as you just had your period.
It is common in teenage girls for your cycle to be un-regular and for you to have spotting inbetween periods - lots of girls need to wear pantyliners just in case.
Tiredness is a common symptom during puberty, as is breast tenderness because the breast are growing and developing, breast tenderness is also common before your period due to the hormones your body is making.
Learn from this fear and either stop fooling around with your bf or get on some birth control - just incase. After all it only takes one sperm, in the right place, to get you pregnant.