Period ALWAYS late. Need advice!

Hey girls.

I really don’t know what to do, throughout my life my period has always always been late. Sometimes I have about 4/5 periods a year and it’s getting stressful because I don’t know what’s wrong with me. When I do bleed it’s only for a couple days and usually very painful and heavy. Sometimes I’ve had a period which lasts 3 weeks. I started my period when I was 14 and I’m now 21 nearly I thought they would have been regular by now. I have tried contraception such as the pill and the patch to try and have a regular period each month. Doesn’t really work. I’m not on any contraception now and haven’t been for 4 year because it just plays around with my body. I have been to the gp several times and after examinations I get no where but they have now put me in for a referral to have a transvaginal and transpelvis scan in hospital next week to check my ovaries etc. I’m so nervous, has anyone had this before? I’m worried that my fertility is going to be low which sucks because I really want a baby next year. Can anyone give me any advice or help my nerves of the examination? I would be very appreciative. Thanks girls ❤️