It is not normal to bleed after sex, no. There is no such thing as your body being used to sex or not, only on the scale of comfort maybe. The body needs time to get ready, for a lot of women they need mental stimulation as well as 30 minutes of foreplay on them before they are ready for penetration. So be sure not to continue if you feel any pain or discomfort. Having sex when your body isn’t fully ready will result in vaginal tears which cause bleeding.
However, irregular bleeding is very common while on birth control so it’s possible you’re experiencing that. This bleeding cannot be controlled but is more likely during the adjustment period of 3-6 months.