blood in semen

I'm very embarrassed about posting this, but I am worried out of my mind and need to speak to somebody.
About a week ago my wife and I had sex, when I climaxed I noticed my semen was a dark red and rusty color, The sight of it nearly frightened me to death to be honest. I went to see my GP who did the usual examination, rectal prostate check etc etc, he wants blood an urine samples which I have now given, got to go back and see him in a week. Now just before xmas they found blood in my urine during a routine check up, its not visible, can only be seen on dipstick test, he sent me to see a urologist at the hospital, they did a ultrasound scan and a cystocopy, plus they checked my prostate again, they said everything was fine and they could find no cause of the blood in my urine and to just forget about it, as in some people it is perfectly normal to have a higher than normal amount of blood in the urine.
And now for this to happen is very frightening, I've convinced myself I have cancer.
Wouldn't they have seen anything suspicious on the cystocopy or in the numerous blood and urine samples they took. My gp said he's not over concerned if it's a one of case and if it is to simply forget about it. Thing is now, I'm that scared I can't get an erection to find out. (I also suffer from sever depression and OCD) because of that my wife and I do not have sex very often, maybe once a year if were lucky, the antidepressants have stopped me from getting an erection except sometimes I can but not very often. I'm male 58 years old.
any help advice greatly appreciated
vangellis