Going to see your GP is a very good idea and start. Try and be very honest.
I have lived most of my life in the UK, so I do know the NHS system and it is different to over here.
Here in the US they would draw your blood over the phone when you make the appointment if they could
. But that is a good thing, they need to know what's going on and so do you.
Don't worry too much, it will only scare you more. You are doing the right thing.
Keep us posted.