@acaciabluebell yes that all sounds about right. This doesn't mean 'you are infertile'. It just means they need to do some checks to see if there's anything that needs treating. I remember feeling the same - I was crying in the bathroom at work when my DH said we had a referral to the fertility clinic but actually it just means you can either get some answers or get some treatment. It does NOT mean you can't have a child.
As for the rest, I'll talk you through:
Day 21 tests - as your cycles vary, I would suggest using OPKs and booking the test for 7 days after ovulation.
I'm not sure exactly what they mean by 'internal examination' but maybe that collectively means swabs and scan? The swabs are just to see if you have an STI (interestingly I don't think they check the male for this, but maybe SA would show any ill effects from one?!)
The scan will be an internal scan of your uterus. It's a little uncomfortable but it's totally manageable and nothing to worry about. They will check your lining thickness, follicle count and the shape of your uterus.
To be honest they did nothing more than this at the fertility clinic for us. If by that point you have been trying for 2 years without a pregnancy (it resets after a mc, up to 3 MCs) then they should offer you IVF/ICSI whichever is best suited to your needs. (Eg, if SA flags up problems with sperm then they may be more likely to go with ICSI). Hope that's clear by ask away if you have any questions!
@Bramleyapples13 yeah men can take it too. My husband took 200mg per day. There was 40mg in his fertility supplement but he took extra (I took 400mg). It's supposed to improve sperm quality, but is also good for heart health and loads of other things! I'll definitely be taking it anyway if we ever get past this whole TTC/pregnancy thing