robbyclouds

Hello everyone, iv been.vaping for a couple of weeks now I have a kangertech mod 50w with a arctic horizon tank, now I have a question when I first bought the tank I broke it in at 30w, now 4 days later im at 50w but when I purchased the tank the hits were smooth and I could pull on it for a good 10 seconds or more without even feeling it at a full 50watts, now I can pull it for only about 4 to 5 seconds and hurts everytime, what could cause that.. do I need to get a new coil?