low room temperature

Hi all, We moved into our house earlier this year in March, and at the time we obviously had the heating on. However, at times when the heating wasn't on, I noticed that our two storey extension (one large lounge, one hallway with skylight and stairs, and one bedroom) was absolutely freezing...

I'm after a bit of advise. I couldn't find anything relating to this specific query, apologies in advance if this description is a bit vague.. First thing first a confession, my stupidity originally may (or may not) have caused this. We moved into our new (first) house and in a flurry to find...