Go to a hardware store and buy the plastic wrap for your windows. It consists of two sided tape that you put on the inside window casing. Then you lay the clear plastic unto the tape. Then you use a blow dryer and the clear plastic will shrink until it's tight and if done correctly you will be able to see out of the window with no distortion. This will stop most of the cold from coming through your windows.

This alone can increase the temps in your room and take away the draft that you are feeling.

Good Luck!
Jim Smith