I'm a 3rd for jlks answer. Water quality is most likely your problem by the sounds of it.
Like jlk asked, do you use water conditioner (to rid the water of chlorines and chloramines) on your tap water before putting the fish in?
Does your city's tap water contain ammonia as well as chlorine?
Be aware that some conditioners don't detoxify ammonia, be sure to get one for all 3, chlorine/chloramine/ammonia.
You may also be dealing with toxic levels of nitrite too if you haven't cycled the filter media.
Once you have a master test kit, test for ammonia and nitrites first. If you have ANY nitrites, buy a bottle of nitrite detoxifier too, and dose accordingly. NH3
/NH4 should be 0 too of course. Nitrates 5-20ppm
Keep up with water changes.
If you have dirty water, no medication will work on the fish.
and when you raised the temp, how high is it, and how did you raise it?
Being a coldwater fish, if the water is too warm, unlike tropical fish it will have an adverse affect and lower the fishes immune system. I hope you slowly raised the temp too, like 1C each hour or so.
Please keep in mind, that a comet will never be 100% healthy in 10g.