I really feel for you as it becomes a vicious circle and the more you worry about not sleeping, the less you can sleep.
I'm sure you've had all sorts of advice already but one of the most important things is to stick to a sleep regime. Go to bed and get up at the same time every night/day. Do the same 'wind down' things every night, so that your mind and body realise that sleep is coming.
Most importantly, but really hard, is get up at the same time every morning and don't be tempted to lie in to catch up. Eventually, you should reintroduce a good sleep pattern.
Hope that helps. Sleep well!