Thanks for posting your query.
I can understand your concern for the burning sensation in penis during ejaculation, discomfort in penis head and pressure sensation in lower abdomen.
Although early tests for gonorrhea and Chlamydia have come out normal, false negative test results can also be there. Hence it is important to rule out urethritis. Urethritis means inflammation of the urethra and is mostly gonococcal or non gonococcal ( mostly caused by Chlamydia). But it can also be caused by non infective causes like trauma, allergy to soap, spermicidal creams and deodorants or due to urethral stricture. It mostly causes dysuria, a white/cloudy discharge and a feeling that one needs to pass urine frequently, discharge from the penis, burning or pain when urinating, itching, irritation, or tenderness, and underwear stain.
Hence it would be wise to opt for specific tests for Chlamydia which include Nucleic acid amplification tests (NAAT, to find the genetic material of Chlamydia), Nucleic acid hybridization tests (DNA probe test, Enzyme-linked immunosorbent assay (ELISA, EIA), Direct fluorescent antibody test (DFA) or chlamydia culture.
Other than that prostatitis and interstitial cystitis should be ruled out. The typical symptoms of prostatitis are fever, pelvic, testicle, or rectal pain,frequent and painful urination and ejaculation and incomplete emptying of bladder. It is also possible that sitting on an inadequately padded surface or for prolonged periods of time is causing transient irritation to the prostate. This could be appearing as the pain in the penis head. To rule out prostatitis get a digital rectal examination of the prostate or your PSA levels measured.
Interstitial cystitis or painful bladder syndrome is a chronic condition. Symptoms mostly include lower abdominal pain, pressure in the bladder and/or pelvis, frequent urination and dyspareunia. There is no specific test for interstitial cystitis but various investigations may be done to rule out other similar conditions. Cystoscopy and biopsy may also be done.
I suggest you to get evaluated for these conditions from a urologist.
Hope that this information helps and hope that you get better soon.
Wishing you good health.
A couple of things I forgot to add. I am 29 years old. When I get the feeling to urinate, it quickly becomes uncomfortable if I don't urinate right away. I get this pressure in my lower abdomen.
So even with 2 negative chlamydia tests it is still possible it could be chlamydia? Are all the things you have listed easily treated with antibiotics?