Young age having trouble conceiving ?

Patient: I’m 19 years of age, been Having unprotected sex with my partner who is 24 for 3 years , he has two children already so I know it can’t be him my periods are all over the place I could have a period on and off one month then no period the next have terrible pains throughout the month irregular bleeding . I’ve been to the doctor and was told because off age and because I was perscribed the pill ( which I didn’t use) they won’t answer any of my questions I’ve tried ovulation tests and nothing is coming up . Really don’t know what to do I’d rather be checked at the age I am now so I’m still young not be Embaressed to go to the doctors about this