Suspected lymphoma. Step i should take?

I am a 22 year old male.I have had fever in the beginning which wasn't going away and then general weakness and flushing.My gp did some tests and he said I have hep c virus.So he started sofosbuvir and velpatasvir for 12 weeks.I  am almost at the end of my treatment but the problem of weakness,fatigue and hyperviscosity of blood came also as a shock and new symptom.The CT scan with contrast shows multiple enlarged bilateral axillary lymph nodes and multiple mildly enlarged periportal(12mm largest in short axis)and aortocaval(largest 9mm in short axis) and the spleen is mildly enlarged in size (11.5cm) and also few subcentimetric mesentric and para aortic lymph nodes seen.I have had black spot in my leg which isn't going away after 1year.Even if i sleep 12hours a day I cannot walk properly.All other blood reports are normal.CT of brain and chest is normal as well.Is it lymphoma or melanoma or what can be done to confirm it ?what is the next step I should take ?