Why do I have to keep resetting my SMC?

Unplug the charger from the electrical outlet for a minute to reset the internal circuitry of the power adapter.

If you have a touchbar MBPro, then try connecting the charger to a USB-C port on the other side of the laptop to see if it has the same issue. If it works on one side, but not the other side, then the I/O Board is bad, otherwise it may be a Logic Board or Battery issue.

Like @Kappy mentions the Logic Board has a 90 part warranty on it so you need to take the laptop back to have it examined.

Take it back to the technician who worked on the computer. He/She should warrant their work for a period of time. Given this appears to be a hardware issue, there is nothing we can do to fix it for you.

We are users like you. We have no access to your computer for evaluation. It is impossible to say what hardware is at fault and what it would cost.