no sleep at night

i have had a turp surgey, its help me during the day, but i am having to get up at night about 5 - 6 times to void always with a erection when i void the erection goes away this goes on most of the night, what a headache, then when the erection stop an the urge to void  goes away which is about 7-8am if i sleep late then i start hurting in my stomach bladder area have to get up, once i get up in a  upright postion the pain an erection goes away by the way my stream is good an i pretty sure i am empty out during the night, during day right after i void sometimes i feel a strong urge to void again 2 steps out of mens room when i know ive emptied out i also feel like somethings pressing against my bladder some times when i walk, my urologist dont seem to be to concerned, i am taking saw palmetto an 10 mg hytrin ,does taking alpha blockers help after turp? how about saw palmetto, it seems like  the hytrin helps me to void with the erection im having during the night also have touch high blood, can anyone tell me why im having erection each time i have to void during night ,better still why am having to void 5-6 times night?,i like to hear  from anyone.