I feel exsessive daytime sleepiness even though i get enough sleep (this lasts for2months). i also experience headaches, brain fog. ive done many blood tests, they all turned out negative. can my dust mites allergy and vitd deficiency be the reason?

Get sleep study: There are many possibilities with excessive sleepiness. One that is commonly missed is a sleep disturbance called sleep apnea, among others. It these your system does not enter the deep sleep level needed to restore your system even though you "sleep" for a normal duration. It is something I would look to long before considering allergies or vitamin deficiency.

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!