Prostate or anal pain. Serious problem?

Hello I feel pain or pressure like feeling in area  under penis and above anus...it don't stay for long and if I drink enough water then mostly no pain or no burning or problem in urinating...but if I drink too less water then I get very less urine then it feels to give pressure while urinating and sometimes burning only in starting urinating...feels urine has come to urethra but it is being stopped or blocked by something and then it suddenly comes and burning goes..and relief... I think I'm suffering from hemorrhoids  ..anus feels swollen and very tight and inside anus there are small like things...are this hemorrhoids? I hurt by back by falling down on stairs which caused pain in bones around anus ( don't know what it is called ) and bone between end of back and start of butt (in center) In morning I get full bladder and bladder pressure...feels I'm backing my penis and tighting it too much which cause pain... Is this prostatitis or any other serious problem? pleasetellimso stressed