Plan B

I’m on birth control that I started 3 months ago but it’s been making me have more periods. Like I’ve had 4-5 periods in the last 3 months and i had sex with my boyfriend on Friday night and he came inside me. That was the first time I’ve ever had that happen and so i took a plan b the next day but an hour or two later I got overly tired and all day today I’ve been sleeping. Is it because of the plan b? Does that make you tired? Or does it mean that it’s working? Please let me know!