Why am i always tired?

i go to bed at 1 am earliest, 2 am latest, and get up usually 11am or 12 pm (im 16) and recently i have been quite tired day in, day out. my nose has been a bit runny, and my back has been quite itchy with a rash (this might be an allergy, as it happens in one part of my house then fades when i leave)...but im worried about the possible symptoms leading to something serious?