Hello and welcome to the forum. Thanks for your question. I'm glad you have seen your doctor and always follow up with them if you are concerned. Viruses can last for a good while. Two to three weeks is not uncommon. Your symptoms are indicative of a virus. https://www.mayoclinic.org/diseases-conditions/respiratory-syncytial-virus/symptoms-causes/syc-20353098. This is a very common respiratory virus that many get.
When you have a virus such as cold or flu or rsv, it's important to take care of yourself. You also need to watch for secondary infections. This is when bacteria does form in sinuses, lungs, ears, etc. This would be situations like sinusitis, bronchitis, pneumonia, ear infections. With these types of secondary infections, you become worse in terms of how you feel. It usually is quite noticeable. Taking something like Mucinex helps prevent this as does drinking plenty of fluids.
Hope you feel better soon.