。
My head is still pounding, but the fever is gone.
Literal
Still head [topic-は] pounding-[progressive-する][but-けど] fever [topic-は] already not-exist [emphatic-よ].
がんがんする is a 擬音語 for a pounding, throbbing headache — the sound/sensation of intense rhythmic pain. 熱はもうない 'the fever is already gone.' Contrastive は used twice — head still bad, fever gone. A health update after being sick.