Why do i get small little rash bumps at random times an they itch an hurt really bad. then after a little while they just go away.

Don't just say rash: Before any health provider could answer your question you need to add more information. The skin is the largest organ in the body and is exposed to the environment, viruses, other infections, chemicals, dryness, etc. It shows how is your immune system reacting and internal conditions. Tell us more: where is the rash: lip? genital?, how often appears? , does it have tiny blisters ?,etc,