Pregnant Girlfriend all of a sudden not sure how she feels about me?

Honestly it really could be hormones. Some women get them really bad and will hate someone and love them constantly. It doesn't mean that she doesn't love you she is probably just feeling strange. After about 12 weeks the baby starts using it's own hormones and doesn't need to use the mothers as much so she may start to feel better and more normal so she may start acting different. I will point out that you have only been together 5 months so give it time. Be there for her and let her know you want and love this baby and her. Pregnancy is hard and it effects so much in a woman so all you can do is be patient. Good luck