Smoking weed and cigs together is worse than smoking either by itself.

Weed smoke is hardly good stuff to have in your lungs, it is full of nasty nasty stuff, but a healthy set of lungs can take care of it no problem. That's why when you smoke a lot of weed, you cough up a lot of phlegm, that's your lungs doing it's job.

This is primarily a function of the cilia in the trachea, the little hairs, that accomplishes this. Now here's the kicker, nicotine puts the cilia to sleep basically, severely limiting your lung's ability to get rid of the tars you get from smoking any sort of vegetable matter (yes, even lettuce). That's why a cigarette smoker's cough is an unproductive and shallow one compared to the weed smokers heavy and productive cough.

By smoking cigarettes on top of weed you rob your body's ability to rid itself of the nastyness that you get from both and at that point when someone says "smoking weed is harmless", that doesn't apply to you, because that sort of adage is only applicable to those weed smokers with healthy lungs. Weed smoke is very potentially harmful (just how harmful is difficult to say because studying weed and it's effects has been very difficult due to the nature of the political environment that determines this sort of stuff, but we can make generalizations about smoke in general. some of the most harmful carbon molecules that result after a fire are also some of the most simple and any kind of smoke from burning plant material is going to be full of that kind of stuff)

So by quiting cigarettes you are doing a Very Good Thing. you should start to feel better immediately, even sooner if you cut down on how much weed you smoke (i know, i know, it's the worse time to do it!) to let your lungs catch up.