Why is my hearing stronger in my left ear than my right?

Whenever I put on headphones to listen to music, the vocals, instead of being centered, sound like they're coming way more from the left than they are from the right--same with any low frequencies, such as bass-y sounds. I have seen the doctor various times for the problem. The first time they gave me pseudophedrine to get rid of any possible fluids obstructing the ear drum. Then, they gave me an ear levage. It didn't solve the problem, so I had a hearing test. The hearing test came out okay--I heard some frequencies stronger in the left, some frequences stronger in the right, some frequencies the same. The differences were usually minimal--5db to 10db. The doctor also did an air-puff test to see if my ear drums were moving well. He checked everything and it all checks out. There seems to be nothing wrong with me, but clearly I can tell my hearing is offset. He doesn't know what's wrong, but he didn't seem too worried. He thinks that this is an odd occurrence, but that it will correct itself over time. He said to check back after around 4 months if it doesn't. He also said that if I was still concerned, I could set up an appointment with an ENT specialist. What should I do?