Hi
If you are only here for six months I am not sure if you can register with a GP. My husband and myself have just recently registered with the Spanish health system, but we are here permanently. I do not know what your situation is, but we are retired. We were able to apply for a sanitaria tarjeta for pensionistas. To do this you have to contact the UK pensions department and they will send you a S1 (I think that is it). Then when you are here get a form from the local town hall (Enpadronimiento)_showing you are living there. You will also need a European citizens card from the police station, then go to the local social services office and apply for the tarjetas. When you have the targeta sanitaria you can register with a GP. Quite a palava, so will list in order.
SI from UK pensions office
Enpadronimient from Spanish town hall
EU citizen card from police station
targeta sanitaria from Spanish social services
Register with local Cap Salut clinic for local GP services.
I cannot suggest what you do if you are not UK pensioners. Normally you would not register with the local health care system until you are here for six months and can register as a resident. Then you would pay for healthcare through your salary if you are working. I assume you would need to take out private health care but this would not necessarily cover you for everything.
As it is only for six months, It would pay to get any thing like breast screening, cervical cancer screening, any regular checkups etc done before you go to Spain. Then use your European health card for anything that crops up. I have binned my card now as it was no longer valid so cant remember how long it lasts. If it is 6 months I would suggest you just use the card, as it is very long winded and can take a month or more to register here.
One thing here is that you can get a lot of things over the counter that would be on prescription in the UK. If you are on any repeat prescription take it to the chemist and there is a good chance you will get it. And they are not expensive. If you are not a pensioner you will get most things for about the price of a prescription in the UK.
I think if you are not pensioners and not planning on working in Spain then take out private healthcare insurance is the best way.
Hope this may hel a little.