Why do I feel all weird and hot inside?

Please keep anon. I was Facebook stalking a girl I knew (just, because I was bored)and I saw my ex come up as a mutual friend. Now normally, I learnt to kind of ignore it but it now seems that she has changed her profile picture, don't know why that matters I think that's just what caught my eye, but after seeing her little "thumbnail" I went all weird and hot inside. It's been well over 7 months now since we broke up and recently I felt that my mind has been off everything and I thought I was over her. As I struggled getting over my ex if I saw something that would remind me of her or I saw a post on Facebook or something, then I would spend ages just thinking about her and wanting to contact her and speak to her and stuff. Now that I just saw this, I don't necessarily want to contact her as I think I've kind of hate her now, but like my heart stopped and I went all hot inside and I got a weird feeling in my stomach. What is this and why did it happen? Is it going to hinder me getting over her? I'm really worried that I'm going to think about her loads again and not get over her properly. I thought I was over her and I had forgotten (kind of about her). Why do I feel like this?

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