The pain in lower abdomen and frequent urination are the symptoms of urinary tract infection with cystitis ( urinary bladder inflammation). The Nausea and clammy skin is due to bacterimia or septicemia associated with sever infection. Intercourse and Sexually transmitted diseases ( venereal ) may not have to do anything with this. I would advise you the following: Urine-Routine, microscopy , culture and sensitivity tests Blood -complete blood picture Ultrasonography to start with , if there is any suspicion CT scan to confirm. The treatment will be long enough if you want cure. Broad spectrum antibiotics and supportive therapy, bed rest, abstinence from intercourse, plenty of oral fluids. helps early recovery. Urethrocystoscopy may be required in a later date is necessary.