It's winter here now and this is the only time it happens. Some days I won't get any water up to my room on the second floor. But also sometimes the pump for the toilet won't start running? I have no idea about plumbing so could someone diagnose the problem for me?

When it is cold out and goes below say 15 degrees it is a good idea to keep your cold water faucet turned on to just a bit more then a trickle. The cold water flowing keeps it from freezing. I live in a mobile home in colder climate and find this works great. The problem is when the water is not flowing. If you have kitchen on first floor keep cold water flowing there and keep cold water faucet on 2nd floor on also. You don't want frozen pipes as they may burst and case a lot of damage.