Iv Got A Cold Tree Weeks Ago But It Knocked

Iv got a cold tree weeks ago but it knocked me for six .I am normally fast at shaking these things and don't complain when i get one and I got this and its not like no other cold its like a flu with it and this is 3 weeks later and iam still feeling the effects of it but I also have this cough that is not lifting is there any suggestions what I could do please.