People are living longer and closer to one another and are more likely to ask for medical help than in the past. Therefore, modern people are more likely to suffer inconsequential ailments, such as colds and sprains, along with an array of other afflictions that come with age. These folks are also more likely to ask a pharmacist for medicine than they would have decades ago, when many families depended upon folk remedies and home brews. Your perception that more people are getting sick for longer periods may be incorrect. Actually, we are all leading healthier, longer lives than ever before in history.
Drugs unquestionably have the potential to alter the body's immunity.
Perhaps, as you suggest, this is a factor. However, my impression is that most medicine is not the cause of the phenomenon you describe. Be sure to mention the title. As you may have heard, there is a lot of pressure on people my age to have sex. In order to avoid the risks of sex, many of my girlfriends masturbate instead.