Engine Problem - Vauxhall Astra 1.6 Petrol

Hi,
I have an engine problem with my Astra 1.6 Petrol Car.
Firstly, the engine was burning the oil very quickly, I put in 3 litres to the full mark on the dipstick, and then a couple of days later, including some motorway driving, the dipstick was completely dry. There was a misfire last week (came up on the engine management after I got it looked at by the garage) and last week I have noticed that when the engine is started there white / blue-ish smoke coming from the exhaust (mostly white though). Also, I noticed today that the temperature gauge seems to rise slowly when the engine is on idle and not pressing the gas. A couple of garages have said sounds like an engine problem, cylinder, piston or a new engine. Does this sound like the case, is it serious?
Thanks
Mr. P