My girlfriend (18f) and I (18m) had sex and it turns out she didn’t want to. What do I do and how do I deal with this?

My girlfriend and I had sex and afterwards she sends me a text saying that she’s been feeling weird lately and doesn’t want to be intimate for a while. She said that isn’t nothing that I am doing. This was a complete blindside because yesterday she was asking for some along time so we could “study” (joke we have when we want to be intimate). I can’t believe that the whole time we were intimate today she didn’t want to be. I asked her if she was feeling like this today and she said yes and she didn’t say anything because she didn’t want to be a “bother”. I don’t know how to come back from this. We have been dating for over a year and I can’t believe she is not comfortable enough with me to tell me. I feel like an idiot and gross and creepy. I want to say that everything that happened seemed consensual. She removed my clothes and her own. No point did she seem like she was not enjoying it. I don’t see myself being comfortable being intimate again with her again. Like I will always wonder if she actually wants this. Yesterday even when we were doing things below the belt and I asked for her consent to touch her down there and she said yes. I don’t know what to make of any of this. Any advice would be appreciated.

Edit: I should clarify this was not our first time having sex