Engine Coolant light

I've had this problem with my engine coolant light for quite sometime. I don't know if it's serious or if my sensor is failing. When I first got it, I thought it was low and so with the help of my dad, we replaced the engine coolant. After a week or two, the light kept appearing even though there was plenty of new coolant. Sometimes it goes away as I drive and other times it just stays on. I don't if somethings wrong, I've checked so many times but everything is fine, I'm somewhat worried.