Fever, lymph nodes, stomach ache, diarrhea, malaise, headache, fatigue, body ache, protein in urine, very tired, night sweats - for 4 days. what could be the reason? do i need immediate attention?

Yes.: Usually, acute infection involving more than 3 body systems turns out to be viral.. Also MOST of the symptoms you describe are very non-specific in nature, However, your symptoms sound quite severe, so you do need medical attention. Altho I don't know how you know about it, I am particularly concerned about the protein in your urine.

Yes: If you have all these symptoms , you should see a doctor even though they may all be caused by a viral infection. You didn't mention how much protein is present in your urine - the major reason I urge you to check with your doctor since viral infection usually fades away in about 10 days.