What Causes Lack Of Sex Drive In Men?

hello Dr,I am 23 years old guy. I have some doubts about my sexuality. I feel may be i dont arouse for sex as a normal guy of my age would. I had done quite a bit of masterbation in my ilfe and i feel may be thats the reason i dont feel that much aroused now. my penis does get hard but not as it used to when i was 16-17. also it doesnt get hard completely on its own. I have to rub it with hand to bring it to its erect state. Also, after cuming once for long i dont feel aroused easily. I dont know if there is something wrong with me or not. Hopefuly u will be able to guide me from here.Thanks!