"Do different strains make you cough more or less, or what else could be the cause of this? Is there a strain you can recommend that is easier on the lungs?"
How are you smoking your medicine? Are you using papers, a bong or a glass pipe? You may be inhaling particulate matter and those particles have no place to go so they are being thrown out of your respiratory tract. It is important to look at what you are coughing up.
It is also important to understand that’s the only place we absorb cannabis in our respiratory tract is in the lungs, not the mucous membranes of the mouth, nose or throat. Many people take huge hits off the cannabis so even their cheeks are bulging but that is a waste of your medicine and you’re more likely to inhale particulate matter that will trigger coughing. Take much smaller hits and suck air in after the cannabis to get it down into the lungs where it can be absorbed and then below that breath out immediately because it was a smaller breath, nothing was wasted and you can afford to take another hit. When you waste your cannabis it becomes expensive as well as making you cough.
Consider throwing the papers and the bong away. Most bongs are filthy and maybe contaminated with bacteria or fungus and the lungs present the ideal conditions for those dangerous organisms to grow and thrive, to your detriment. A long glass pipe that is cleaned frequently maybe ideal for your use but vaporizing is even better.
Be certain your cannabis has been tested for contaminants and never smoke in metal.
Remember, long term, chronic inflammation, like overheating the lungs, can cause cancer so you always want to smoke wisely and protect your lungs. Do not smoke propylene glycol, a thinning agent used in some vape pens and inhaled, propylene glycol does cause cancer.
Smoking cannabis every day or even several times a day 10 fill your receptor sites and you will notice more coughing indicating you need to take a cannabis holiday because smoking more will have a limited potential to get you high until you have cleaned the receptor sites.
This is great medicine, learn to use it to your advantage, not your detriment.