I dont get periods on a regular basis. i havent in a few months. me and my boyfriend had sex monday, and i started spotting. and then i starting full on bleeding the next day and cramping just like a regular period. is that normal?

Irregular periods are usually very unpredictable and the timing here sounds coincidental. Sex will not bring on a period though it might cause you to be aware of it a little earlier. Trauma during sex can cause bleeding though it presents differently. If you were pregnant than sex can cause bleeding in various situations and even precipitate labor in the later stages.