Believe it or not, slightly leaky valves are relatively common. The severity of the issue depends on which valve is leaking and how badly it leaks. Severe leaks can lead to an overworked heart because the heart has to pump the normal amount of blood plus the amount that leaks back in from the valve. Often, mild leaks are not sufficient enough to cause problems. For this reason, they are generally watched with periodic echocardiograms to be sure they aren't getting worse.
If the valve does get worse to the point that it will be a problem there are surgical repairs or replacements that can be done. If the valve isn't leaking to that point, medications can be used to help decrease the amount of leaking that occurs and help protect the heart some. The specific medicine used again depends some on the valve affected and its severity.
I suspect that in your case, given your leak is mild, your doctor simply wants to follow this over time and see what happens. It is entirely possible that this may never worsen and never be a problem for you. If it does begin to get worse there are other things that can be done.
Advice and opinions given are based on the information provided and must not be considered an official medical recommendation. The limitations of the internet prevent an appropriate evaluation. Always consult your doctor if there is concern.