Welcome to our Forum. I'll try to help. It sounds from your description as though your symptoms were those of non-gonococcal urethritis (NGU), the most common male STI. While chlamydia can cause NGU, most is not and the precise cause is often unclear. The therapy you received, doxycycline is a recommended therapy which is highly effective. On those occasions when dozy does not work it is recommended that the person be re-treated using a combination of a single 1 gram dose of azithromycin plus 2 grams of metronidazole so the retreat,ENT you received was almost that which was recommended. There are several things to do from here.
First, you should establish if you do have urethritis or not. I suspect the clinic where you were seen can do this. If urethritis is (still) present then I would start with re-treatment as described above. If not, then I suggest you look for other, non-STI causes. I suspect the clinic you were initially seen at can guide you in this. The place to start however is with getting tested for urethritis. The best specimen for this is a urethral swab specimen although a urine specimen collected just as you begin to void can be used as well. In either case, it is best if you have not urinated for at least an hour before the specimen is collected.
I hope these comments are helpful. EWH