I need help sleeping.....?

For about the past month/six weeks I have had difficulty getting to sleep at night. I am having some marital problems and am under quite a lot of stress at work and I don't seem to be able to get my brain to switch off - I just keep thinking about the things that are bothering me and they go round and round in circles in my mind. Because I can't sleep I struggle to get up in the morning which means, while I haven't actually been late to work yet, that I end up rushing around at home to get ready in the morning and I get to work feeling even more stressed. I feel distracted and forgetful nearly all of the time - I didn't feel like this before I started having problems sleeping. I am starting an Open University course at the end of this month and I really want to try to get something in place to sort this out before then. Can anyone offer any advice? I would be really grateful.