Frequent peeing?!

Hayley • 18, in a relationship 😸
For the past 2 or so months, my bladder has become extremely sensitive. I used to only need to go to the bathroom maybe 3 times a day. Now I'm going close to every hour! Lastnight I got up 5 times to pee!! 
I'm 18, I'm sexually active with my boyfriend for the past 3 years. We're both clean so it couldn't be an STI. I've also been on the pill for 3 years and take it perfectly so I doubt I could be pregnant (although haven't taken a test yet).
Has anyone got any ideas on why this is happening?