I think jamesneedstoknow was right on! I know I did the same thing shortly after my younger brother died 2 years ago. I would suddenly see men everywhere that reminded me of him. Not that they really did, but in my mind there was something that wanted me to see things in them that reminded me of him. I think it is just the human psyche trying to deal with the loss. There's nothing wrong with you, it seems to be a common ocurrance when you've lost someone you love or were close to. It's just a part of the normal grieving process, we all have to go through.
You have my deepest sympathy on the untimely death of your son. It's one thing to lose a parent, but a child is something you will never get over. You just have to take everyday as it comes and don't remember their death, but rather all the happy years you spent together and the wonderful times you had. Embrace those memories and it will help you to get through every day and know that you had that time together, that some people will never know. They may be gone physically, but in your heart they will live forever!