I have a low fever around 99 to 99.5 every evening and waekness whole day for 2 months, all test by are normal, any hidden infection it might be?

Yes, it could: It is very difficult to answer your question meaningfully, because it remains unknown what tests you had done. Very generally, low grade fever that appears cyclically ( every evening), could indeed be a hidden infection (e.g. Tb), but it could also be one of numerous other illnesses. This is why you need close and continued follow up by your doctor. Stay in close touch with the doctors.

? fever: This may be your normal temperature. 99 is within the normal range and depending on when you take the temperature, 99.5 may not be abnormal. Counter-intuitive as it may seem, exercise may help. Start with low intensity exercise such as walking and gradually increase the intensity as tolerated.

Biorhythms: The body normally cycles through a range of temperature every day.You will generally be at your lowest after sleep slows your metabolism in the wee hours of the morning (0400 for many) and highest in the afternoon/evening (4-6PM for many). Since you list a temperature in a relatively normal range it could be normal. Monitoring your temperature suggests you suspect illness which could also be true

Low grade fever : https://www.healthline.com/health/persistent-low-grade-fever Also rarely Kawasaki disease even in adults. Check CXR if not done already , thyroid antibodies, thyroid function, CRP, CCP levels (PPD as noted previously if not done) . f/u /w / rheumatology and hematology/ oncology.