Ask your bike shop to check your wheels for "true" and "dish".

"True" means the wheels are straight -- they don't have bends in the rim. Problems are corrected by tightening and lossening the spokes. It's hard -- let a professional check it if you don't know how.

"Dish" is akin to alignment in a car. When your car pulls to one side, often the wheels are not aligned, and you take it to the tire shop to fix that.

On a bike, if a wheel rim is not properly centered over the axle hub, the bike is not properly aligned and it will tend to pull to one side.

I learned this the hard way. I bought a new bike after going twenty years without one. I thought I was just old -- I rode like a drunken sailor, always veering off to the right. After lots of trial and error, I learned that the rear wheel was not properly dished -- it was off-center -- causing the bike to pull to the right. I fixed that, and I've been riding straight ever since.