Thank you for reaching out to healthcaremagic.
With the symptoms you describe, i wonder if you have any difference or problem in the way in which you move your bowels. Sometimes this could be an inflammation of the intestines which resolves very well with the correct antibiotic meant for the intestines. The antibiotic for the UTI may not cover this infection.
This could also be likely what we call as a Pelvic Inflammatory Disease
(PID). In that case you would have reported some vaginal discharge/itchiness/smell. This respondes to similar antibiotic as the intestinal infection.
Therefore the first step would be to be in touch with your doctor for such a discussion and antibiotic if he/she feels so on history and examination.
The tightness could be due to fluid in the abdomen which may have several reasons like PID, liver
problems or an ovarian tumour.
Considering your age group, which is not really over the hill; nevertheless, it may be worthwhile to explore getting a CA125 tumour marker blood test
and a TransVaginal Ultrasound
scan since, as i emphasize repeatedly on this forum, one of the earliest signs of ovarian cancer
are symptoms in the lower abdomen. In your case, however, you DO NOT have bloating
which an important symptom.
Rememeber that most human diseases are a play between the environmental factors and your own stress
levels which influence that part of the genetic make-up of a person which prevents cancer. Please don't allow your worry to change those facors towards cancer formation. Of course, a calm investigation into any problem is justified.