My breasts feel full. i'm on the pill and last time having sex was in may (protected). all periods are normal and on time. are they just growing?

Probably: Pregnancy is very unlikely if you have regular periods since you were last sexually active. It is very rare for a woman to have periods if she is pregnant, unless she is taking birth control pills. Birth control pills can rarely result in regular menstruation even when a woman is pregnant. Your breasts may feel full due to normal fluctuations in female hormones.