Hello,
From your symptoms of inability to pass urine, appears you are suffering from urinary retention.
Urinary retention very commonly occurs in men. Once urine around 200 ml gets collected in bladder, a nerve signal is sent to brain which produces the urge to urinate. Urine passes through the two tubes called urethra. An obstruction in urethra especially in men by prostate produces retention in urine. Therefore, you aren't able to pass urine. You could be having an enlargement of prostate or infection of prostate.
Or mononucleosis has neurological complication where it's a possibility the nerve supply to urethra is damaged causing retention of urine. To find out what is affecting you, a blood test and urine test has to be done, if PAS is positive then it is due to prostate pathology.
I suggest you meet a urologist. You need to get a treatment soon to prevent any problem to kidney or infection of kidney. The obstruction in urethra has to be relieved soon.