Yes it can be
Helping with his child could also be stress reducing I'm not saying to saddle him with the whole job of looking at the child, but to take his turn helping, even if it's once in the night so that you can get a bit more sleep instead of constantly being interupted.
I think you really need to speak to a doctor about not only the possibility of post partum depression, but also about your child's inability to sleep for extended periods of time.
At 13 months your child should be sleeping more than he is. He should be on solids now (IE: cereals and some fruits and veggies). Talk to the doctor and see if he's getting enough food. Perhaps he's hungry all of the time. Also maybe he's lactose intolerant and is having pain from milk/dairy. It could also be that he's developed a "habit" and knows that when he cries you come running and he gets attention. Sometimes letting a child cry is a necessary thing, especially when it's become a habit.
I am doing much better today. Both D-Man and I got a little more sleep this weekend. DH also took both boys out to play on Saturday and I was able to get an hour to myself. it was nice. Yesterday my parents came over so the boys played with grandma and I was able to get a few things done.
Thank you - everyone for all of your kind words and support. As I said I was afraid to post about this, but I am now glad I did. I am definately going to try some of the suggestions everyone has posted!