Feel like sex is ugly. Help me.

What you are experiencing is a defense mechanism called 'reaction formation'. Your mind tries to defend itself from something that it doesn't want to think/do so you don't feel bad. In your case it's sex. By thinking sex is ugly and repulsive your mind helps you to keep you away from sex.( I assume that you don't masturbate also)          But just understanding the fact may not help you resolve this.You need to change your Beliefs about sex, marriage and child birth. Beliefs are like computer software that runs the machine. Just knowing a software exists won't change anything. You need to change/uninstall the software. To change your beliefs we need see what your beliefs are , how it formed, why you hold to those beliefs and what evidence you have that your beliefs are true.  Once you could see your beliefs critically (how much it is closer to the truth/reality) you can start to change your views that is much closer to the truth. It's easier said than done. Because beliefs are hard to change and you may think that you are seeing your views critically but your views can be baised. Get help from a psychologist who can guide you to change your beliefs and help you see this in a more realistic way. (Changing beliefs takes time)