I don't think the GP will ask a lot of questions it's not his/her area.
You need to check this but
I think because of the autism act you can now complete a short questionnaire (I saw it online - maybe the NHS site) if you feel you are on the spectrum and take it to your GP who will refer you at least to be considered for assessment.
My 6 year old was referred to a paediatrician through her school - who then referred her for assessment - there were several forms for me to fill out about how she coped with change / when she started talking / walking / her behaviour / ability to hold a conversation / eye contact and her ability to maintain friendships, etc.
We are awaiting for an appointment date for the assessment now, she was first seen in March, but I think we'll hear soon. Depending on your age your Mother will provide a lot of the background for the assessors.