I have had muscle fatigue for about 2 months been tested for covid negative along with antibody test negative, what could be causing these symptoms?

Muscle fatigue: While muscle fatigue is a symptom of Covid-19, it's also seen in many other medical problems including, but not limited to, influenza, diabetes, insomnia, leukemia, MS, sleep apnea, cardiac insufficiency, and so on. I other words, you will require a full examination/evalation by your physician, possible lab tests, possible imaging, to identify the cause and the appropriate treatment. See your GP.

Need to examine: It is not feasible to provide a meaningful opinion without taking additional history, physical examination and may be some tests. It would be prudent to see your doctor and discuss if you may be depressed. Counter-intuitive as it may seem, exercise may help. Start with low intensity exercise such as walking and gradually increase the intensity as tolerated. Wish you good health!

Eval: This requires a workup to determine the cause.