occasionally my 'add coolant' light will pop on for about 5-10 seconds after I've driven the car for maybe 2 minutes. I stop almost immediately every time, check my coolant level and its full all the time. I'm guessing it's my sensor.

so how do I go about fixing it?

 

more than likely you are getting a small air pocket in the cooling system, maybe you have a tiny leak that caused the air pocket or maybe you just need to bleed the system more thoroughly, i would start by bleeding the system again(at the radiator).