I am 21 years old, I want to get pregnant but I have not been successful I have a normal 28 day cycle and I have regular periods, cud anythin be wrong?

Infertility. You and your partner should have an infertility evaluation. There can many causes of infertility.
Maybe. Possible reasons are: low egg supply (diminished ovarian reserve), problems with ovulation including polycystic ovarian syndrome (pcos), hormonal problems like thyroid or prolactin issues, damaged or blocked fallopian tubes, endometriosis, fibroids or polyps inside the uterus, and sperm problems. If you're ttc without success for a year at 21 see a fertility specialist (rei) to get checked out.