As the fever has passed 3-4 weeks I believe you should get yourself investigated well. It can be a flu to start with but no flu will remain so long unless it has been secondarily infected with a bacterial infection.
Or it is very well possible that it may be tuberculosis
as there is fever and night sweats
with weight loss
. Send your sputum for investigations or the lymph
node be excised and sent for tb check.
See a chest physician who can help you on this further