I am going through the same thing at the moment, I cannot sleep for more than 2-3 hours, it is impossible, and quite frankly getting a little irritating. I honestly can't give you any suggestions sorry because nothing is working for me either. I am 37 1/2 weeks and afraid that I'll go into labour and just not have the physical strength to get through it on my own. I have sleeps during the day, I know it sounds stupid because then your less tired for night, but I found my sleeping at night is ruined regardless. I sleep for about 2 hours in the afternoon, do what I can at night (which is quite often less then 5 hours) and then that gives me enough energy to struggle through to the next afternoon.
It sucks - I can only sympathise with you sorry. I wish I knew what to do about it. But you're not alone if that is any comfort!