Portugal has a tax-funded public healthcare system called Servico Nacional de Saúde (SNS). If you are part of this system, most medical services are for free or for a small co-payment. All citizens of the EU with a valid European Health Insurance Card and citizens of the European Economic Area are able to make use of the SNS system in Portugal for their first 90 days. After these days they need to be registered as an official legal resident to make use of this sytem.
Some people prefer to make use of private healthcare. Private healthcare is a more expensive option but comes with the reassurance that you can bypass long queues and waiting lists and offers more comfort than public healthcare.
In Porto, you should not have any problem using pharmacies. Most pharmacies are runned by chemists who are qualified and speak English.
In case of an emergency in Porto, you can make use of the general EU emergency number, 112. People who operate on this phone number usually speak English.