Tinnitus sufferer for years here.
I've learned that tinnitus can be a component of other issues including Ménière's disease which is an inner ear problem with multiple symptoms, including tinnitus, sinus pressure, vertigo, lack of concentration, etc. I've also found that there is a pretty big gap in the medical community on this subject. My MD sent me to a ENT specialist who did a sinus x-ray only to find that my sinuses are clear. The manifestation of hearing loss, plus, sinus pressure, plus ringing can reduce quality of life considerably. Being in a social situation where your hearing is compromised, stuffy sinuses which compounds the hearing problem, and having your ability to focus at, say, 80% vs 100% can make you feel socially isolated. Showing up around people you care about and not being the best version of our yourself is not fun.
There are a lot of explanations for tinnitus out there. One being that hearing loss creates an absence of frequencies that were normally presented to the ear canal, and with these missing, the ear/brain is attempting to replace them. And, as other's have suggested, stress, caffeine, etc.
As far as sinus pressure, I accidentally found some videos on line that provide immediate relieve from this. Involves exercises of the earlobe while breathing, swallowing, opening and closing jaw, etc. Seems to work for me -- immediately.
Related to other Menieire's symptoms, I found a company in India called Biogetica that offers a regiment of supplements that seems to help. I just ran out of one of the supplements and waiting for a refill. It takes a while for orders to arrive from India. I can't say for certain that the results are 100%, but I believe there was some improvement, and the Menieire's symptoms are worse since I've been off the supplements.
Good luck with your treatments/cures.