New RN, self doubt

I am a "new" RN. I started my job as a graduate nurse (GN) in the ICU 2 weeks after graduating nursing school, and after 4 weeks I passed my boards and got my RN. I worked in healthcare as an nursing assistant for 3 years, so although i was a new nurse, i felt confident after observing nurses work and assess patients for 3 years that i was capable of tackling something as intense as an ICU position. I never pictured myself as a medsurg nurse, it just wasnt for me. I am blessed to work with such an awesome group of supportive nurses who all help each other out and I have never felt like I am afraid to ask a question if I am unsure of something. I had 16 weeks of orientation and I have been on my own for the last 7 months.

This my issue: I've never felt anxious about going into work, I still don't, however just recently- I'd say within the last 2 months, I have been double and triple checking everything I do and I go home at night and I lay in bed and think about things I did and if I did them correctly (even though I'm sure I did, because I always check things over again). I've been doubting myself, I am so anxious and work is all I think about when I am not there. I have been reading posts and I know it is "normal" to feel like this at first, but after 7 months to START feeling like this? I cry about work when i am at home, and i question myself constantly as to if I did everything I could for my patients.

When I am at work, I feel confident and sure of myself. I am cool, calm and collective, especially when "**** hits the fan", I do not get flustered or upset. It is AFTER work when I am home that the anxiety kicks in, I've found myself on 2 or 3 occasions already to be walking out to my car and running back into work to check and make sure I did "xyz" or that my patient's heparin drip was at the correct rate (even though I already checked it 3 times before I left). Is it normal to JUST start feeling like this after I've been on my own for 7 months already? I love my co-workers and the work environment, but the way I have been feeling recently when I am home in my own thoughts is a real downer. I start to feel as if I am not cut out for this, even though a nurse is all I ever wanted to be. I love my patients and I truly put their needs and safety first, but WHY is it that when I'm not at work I am stressing out about it?