It does sound like it is getting to cold, the best way that I have seen to keep the temp up is to get one of those liquid filled radiator type space heaters and set it to I guess 22C not sure I am not familiar with celcius. These heaters are very efficiant meaning very low wattage and produce a lower heat that won't shock or burn your plants and are alot less of a fire hazard.

Another way is to go to a 24/0 light cycle for your veg that way your light keeps the room warm until you go to flower. ( I use a 24/0 cycle in my grow during veg.)

LOL and looking good so far.