Your tinnitus is obviously bothering you - like most people on this board (and who can blame you). Here is an exhaustive list of things you can do, as I see it (costs not considered):
1) Have a complete 0 - 16 kHz audiogram done (not easy to find places that do these).
2) Revisit/have a complete tympanometry test done; if you suffered a blow to the head in the "right" place, then perhaps there is a structural problem with your airways. The tympanometry test would indicate whether there is reason to justify a visual inspection of Eustachian tube (done via the nose under full anesthesia). Radiology may also be warranted - but I am assuming you already have had that...
3) Depending on the outcome of #1 and #2 above, see a neuro-dentist for an evaluation of your jaw; the dentist will - amongst other things - stick his/her fingers in your ear (with gloves on!) while asking you to open/shut your mouth. Perhaps he/she will also ask for radiology of some type.
4) Again, depending on the outcome of the above, consider finding a clinic which can objectively diagnose your tinnitus (assuming it is subjective, which is the most normal type ie. nerve damage). This can be done at eg. the brai2n clinic (
www.brai2n.com) or at professor Jeanmonod's clinic in Switzerland.
The above is not going to be cheap, and most of it will only lead to a diagnosis - not a cure. So consider if it is worth doing in the first place. If your head injury and onset of tinnitus is closely linked in time, then you can assume that the injury was the cause of your condition, and if nothing immediately is found by the doctors who examined/treated you, then there probably is not much which can be done. A post diagnosis in that respect is not worth very much, because it is just that - a diagnosis. However, admittedly, there are now experimental otology therapies being developed which potentially could help you - and in order to enrol in those, a diagnosis would (eventually) be required.
Those are my thoughts. I am not a doctor. The above is therefore what you can consider "friendly" advice.