Nether portals not linking

Nether portals are not linking up, I have 1 location in the regular world to go to the nether. When in the nether you go return to the portal, its not the same portal that I entered the nether with, but instead it creates a new portal far away from my base location where I built the portal. The same happens when a new portal is created, instead of the two being linked together, one in the normal world and the nether, it does the same thing and creates a new portal completely elsewhere. This has been going on for too long and nothing has been done to fix this.