English isn’t my first language sorry for any spelling mistakes. 
It started about a year ago, I started to have high/low mood changes. First I didn’t even think anything about it I had high sex drive out of nowhere, started watching porn every day, masturbate 2-3 times a day, even bought toys and still nothing could satisfy me. It’s like I was starving and nothing could help. I am in a relationship for almost 4 years, have sex 1-2 times a week which I was totally fine with for a long time until I had this hyper sexuality feeling I can’t really explain. Also whenever I feel like that I have no appetite. Sometimes I go without eating for 3-4 days and just can’t force myself to eat. I can’t sleep, I’m up until 3-4 am even when I physically feel exhausted, I started taking melatonin but after a while my body got used to it and it doesn’t work anymore. I’m shaking a lot and feel anxious for sometimes no reason. This usually lasts a week or two and “I’m back to normal” If this makes sense. I started writing down dates (when I feel this crazy)  so I can figure it out when is it gonna happen again but it’s sometimes nothing for a month or two then 2 weeks. Whenever I felt so horny I started sexting with strangers online one time I even sent pictures. But as soon as I sent the picture I was just like: what the hell did I just do?? I’m not this person and I feel like I can’t think clearly. My so doesn’t know about it, and I feel horrible that I did that. I’m gonna delete reddit after this post because I feel like some reddit posts make me even more horny and I have to control myself. I know this isn’t me and I don’t know what the hell is wrong with me. Please help