Problem with health cover.

Hello all. Would welcome some advice please.

I've been here 2yrs 3 mths.

First year, was working for co. and paid fully into system, Sept 2016-June. 2017. Had public and workplace health cover.. All good. 

End of contract in June 17, returned to UK for 3 months to work/live and and came back out here again in Oct. 2017..

(Have from outset of my original contract, had  residencia, tarjeta sanitaria and padron.)

So from Oct 2017, stayed ( originally just one more year,) but not working, just volunteering.. Have adequate funds to support myself.  Assumed because I'd paid into system, I was covered for public health system. I now think I was wrong on this and I wasnt. ( Anyway, nothing too drastic, because I didn't use the health service that 2nd year at all anyway so no costs incurred). 

I then decided to stay one last year.from Oct 2018- Oct 2019.to continue volunteering and study 6 hrs pw at the university here. 

However a recent trip to GP here made me think again about health cover and whether I need to get it. ( Has absolutely no probs at the docs re receiving service using tarjeta sanitaria).  I think I do and that ican't rely on my one year's worth of payment. TBH I've never consideren myself to be resident here.. My home, my partner and my tax bills are all in the UK and I'm definitely going back for good end Sept/Oct this year.

So, advice please. Can anyone either tell me I'm wrong and I'm covered from having paid in ( that would be nice!) or recommend medical insurance? Pref for 9 months but realise I may have to buy year.

I just want to regularise things and pay whatever I should be paying.

 (I realise I also have to change driving licence, which I'm in process of doing). 

Many thanks all.