I've been like that (only through the first trimester though) where I was getting shaky everyday around 3pm and it lasted for a few hours. I was certainly not cold (I live in North Queensland and had the a/c going because it was soooo hot) and I test my BSL every now and again to make sure it is okay and it wasn't that either. I don't know why but it did pass after the first trimester and now I am fine. I found it pretty traumatic to be feeling like that everyday as I felt really strange. I think it is just one of those things about how your body responds to pregnancy. I was keeping up my gp appointments and everything was normal on all my tests so there is really no explanation for it.

I hope it stops for you soon