head pressure , wake up exhausted

im a 29 yr old male. i have greatt health and always have. about four months ago i started to get headaches that were main felt on my left side and they would somewhat throb and cause dizziness (but not vertigo dizzy). i also started to have problems sleeping. i would wake up feeling unrefreshed and literally fought with all my strenghth to remain awake. many times i would have to lie down because i could not stay awake and was soo exhausted. i would get 8 hours of sleep, so it wasnt from lack of sleep. this persisted for about a month. the headaches would come and go, but about two months ago, they returned and have not left. i have had every test imaginable done to find a cause (ekg, eeg, mri, sleep study, spinal tap, numerous blood tests), but all came back negative. i had started to develope a bit of anxiety from all of this. the sleep problem subsided about a month after it came, but within this last month has returned. and the headache feels ore like head pressure rather than ache (not like a migraine, which ive only had one once before 8 years ago). so my gp and i have concluded it might be from stress and anxiety. ive started taking generic zoloft at 25mg to help with things and possibly get results. its been almost a week now and things dont seem much better. i do have bouts where im falling asleep but i keep awaking cause my brain feels like its twitches and i awake, but dont jerk with my body. this also was goin on a few times prior to the meds. does this seem like something neurologically wrong, or could there be another explanation? thank you for your time.