1. How long have you had this problem.
2. What is the current charge level of the battery?
3. Does the laptop run on AC when the charger is plugged in? Or does it still run off battery?
A lot of newer laptops protect the battery by not charging it if it's above a certain percentage (usually 90% or 95%). If you plug in the charger at a lower percentage and leave it plugged in, it'll charge it to 100%. But if you unplug it just after it's reached that threshold percentage, and plug it in again, it won't resume charging. You have to deplete the battery below that threshold percentage before it'll charge again.
In the old days, the laptop would charge the battery to 100%, stop charging, the battery would self-discharge to 99% after...