Ok, it sounds like you are tightening the bottom bracket.

With cones, if everything is working right, you have to set them just perfect, not too tight, not too loose.

However, if you have a broken bearing or something, then you won't be able to adjust it quite perfectly. Caged bearings periodically disintegrate too.

At this point, you need to take everything apart and inspect it, and repack the grease, then set the cones, and lock nut.

Do you have one piece cranks, or three piece cranks? If it is the one piece cranks, they can all be disassembled with pretty standard tools. If 3 piece, you'll need a crank puller.