Just clear your mind,think a happy thoughts, your girl do love you, theres nothing to worry about. :) just focus on doing some things,it really works and share your feelngs to your gurl, she will understand it. :)
I think it could be generalized anxiety disorder or it could be due to stress, i think you can consult your psychiatrist/therapist.
Because what I'm experiencing now kinda feels exactly like when I had hocd. Like I would obsess over it all day long and I'd think that my girlfriend will find someone better than me
Is there anything I could do for that?
Your problem looks like "ROCD " which is relationship ocd, but the point is in ocd you doubt on your self, you don't doubt on other person.
If your doubts would have been like whether you love her or not then it looks like rocd but since your thoughts are related to doubt about her feelings for you, it looks like general anxiety and not ocd . It could be your insecurity too.