Girlfriend Sex Life

Hoping to get some female advice for this one, thanks in advance for any feedback.

-So I'm 22 and have been dating my girlfriend of the same age for about 9 months. When we first started dating/hooking up, we had sex frequently, multiple times a week and things were going great. Sex seemed to come naturally for us and just was something normal in our relationship. Now however in the past 3-4 months or so our sex life has slowed down quite a bit. It isn't spontaneous for us anymore and I seem to always have to be the one to iniate it. Sometimes she even seems bothered when I ask or try to iniate it. Noting has changed in our relationship as far as loving eachother and caring about one another, it just seems like our sex life has hit a speed bump. Is this normal? How can I approach her about improving our intimacy without making her feel uncomfortable or offending her?

Thanks guys sorry for the long post