The important question to answer is how long in between have you gone before they have needed to be replaced. Well done veneers that are well maintained can last 10 years or more. If they are being replaced more frequently for reasons other than aesthetics, you may want to have an experienced cosmetic dentist evaluate the reasons they are failing.
The anser is dependent on how long a time frame you are talking about and exactly why they are being replaced. Are they cracking, denbonding, or caviites. Three times in 10 years is a problem, three times in 30, not as worried. If it is the 3rd time in 10 years than I think whoever has been making them for you is not addressing the exact problem. There could be problems with the bite, the type of cements he is using or your oral hygiene may need improvement. Before you make a new set I would talk to your dentist to see what he thinks the problem is