Questions: Relationships

Am I going crazy? My girlfriend's behavior changed significantly in the last month. We are 120km apart from each other so we only meet during the weekends. During the last weeks she started going to sleep at weird times and she is 20. If she has to get up for uni at 6a. m. she goes to sleep at 8p. m. which is 10 hours of sleep and if she has to wake up later she goes to sleep at 10p. m. and wakes up every morning at 8a. m. I would understand if it was only on uni days but she goes to sleep at 8 or 10p. m. on weekends too! And everyday she takes a 2 hour nap which totals to 12 hours of sleep everyday. The thing is that when she says "she is going to sleep" she still active on Messenger for several hours. I asked her about it and she said that she isn't texting anyone because she is sleeping and that Messenger's activity status is bugged. I researched online and that is true that on some phones it is bugged so I believed her. Until she started working. Two days ago she started work at 8p. m. (the usual hour she goes to sleep) and Messeger said she was offline from until she started working to until she finished her job. She can't use her phone on the job. The situation was exactly the same yesterday. So it seems that her activity status is working pretty well. As I said this situation didn't happen before, we would text and sext late into the night even if she had to wake up for uni at 6a. m. the next day. Now the last time we did sexting was z few weeks ago and she used to love it. I understand that sometimes someone needs just a bit of space and I'm not against it but not everyday for a month. She also started ignoring me sometimes, it takes her a few minutes to respond when she is online. When we talk it seems like she is bored etc. Am I going crazy or is she cheating on me?