You are sick, you are in a foreign country and it seems you have no companion to help you. That is not a good situation to be in, but before you put yourself through the stress of navigating a foreign medical system, there are a few things it would be useful for you to know:
Firstly, the Spanish public health system is first rate, as I can tell you from personal experience.
Secondly, a Spanish doctor will prescribe precisely the treatment and medication they regard as necessary, no more no less and will flatly refuse to prescribe anything else.
Thirdly, the best place for you to go to would be a Centro de Salud or policlinico, not ER ('Urgencias') unless you have an underlying medical condition that requires immediate or specialist treatment. Alternatively a private hospital will treat you in the same way as a public facility, but at greater cost. There will be a Centro de Salud nearby (use Google Maps or ask in a pharmacy) although it may not be attended every day if it is in a rural area.
Fourthly, you are Covid positive, consider whether you need to enter a medical facility at all.
Fifthly, some medications may be in very short supply in Spain, unobtainable, or unapproved.
I hope you get well soon. I had Covid in Spain too, so I can understand what it must be like for you.