New Pill - Pregnancy?

Please post anonymously
I changed pills a month ago as per my GP's suggestion because I was having hot sweats. Anyway I have taken the new pill for the last month. I started the sugar pills Monday and the only sign of a period was a little spotting on Wednesday night. I am worried that the pill didn't work and I'm pregnant, or am I being silly and this is just a side effect of a new pill? I will go back to the GP next week but I just want to know what others think.
Thanks Ladies