A cycle of sadness

I have always told myself that I’m not insecure because I don’t have any issues with the way I look and don’t compare myself to other girls in that way. But I’ve realised that I’m insecure about everything else in my life. My intelligence, my friends, my family, my career choice. I’m insecure that I’m going to live a boring life. I’m insecure that I literally have no feelings for any guy and I will never find someone I will fall in love with. Most of the time I’m fine but other times I can’t help but be overwhelmed by sadness, especially when on some of my periods. And most of the time I can’t explain why I feel so sad, I just feel so sad suddenly for no reason. But now I’m realising it’s probably because of these insecurities I have. In a week I’m going to read this post and laugh at myself because I know that this moment of sadness will pass but it’s a cycle and I will get sad again and I don’t know how to deal with it. I know I shouldn’t be insecure about these things but I can’t help it. I’m honestly really blessed with the life I have but why do I still feel this way? I have an exam in 2 days and I can’t get myself to study because I feel so sorry for myself and I hate myself for it. If anyone has any advice I’d really appreciate it. Thank you.