The crisis that is my life

I have not been happy with myself for a while, I suddenly doubt everything, but I'm not sure ...... what a strange one. I've been happy with my boyfriend for three years now. I have a great family and a great group of friends around me, and my studies are fine too. But then the doubt is doubted ..... no doubts about my relationship or just my study, but complete doubt about my life.  Have I succeeded in  everything up to now? What else can I do? Have I made the right choices, I'm doing well? Should I have done it differently? Can I do it differently? And especially  feeling that this is it? I feel insecure ...... and I do not understand that because I know what I have and am happy with what I have. I do not know how to translate it ......... but the best way I can is I’m in a mid-life crisis. But if I look for information, I'm far too young. I just do not know, maybe I just cannot do it, but it just does not feel good.