I have 2 full bathrooms on the 2nd floor of a 20 years old home in Mississauga.

The toilet in one of my bathrooms on the 2nd floor are clogged a few times when we just moved in this house (only a few months ago). We figured that if we flush the toilet more frequent as we do our bm job, then it won't clog. My question : what is the cause of the clogging, the toilet or the waste pipe. Thanks