If the cracking continues to be the result of settling, then your 'fixes' may only be temporary. HOWEVER, if you believe the settling has stopped, then perhaps the cracking is the result of how you're fixing them.
Joint compound / spackling is usually done in layers. If you put too much on at one time, it will not dry evenly, thus, cracking. Sometimes, you need to 'dig out' the cracks a bit and put in the compound. Put in a little at a time and let it dry overnight. Force it way in there. Then as you get 'flush' with the surrounding wall, put on less and less until you get the desired finish. Do sand between the finished layers, and feather it out a little more to the sides with EACH, progressive layer. Just filling the crack won't do. By feathering it out, the compound 'beyond' the crack actually holds the drywall together (a little.) Maybe that's all you need. If it comes back again, consider using fiberglass mesh over the crack. If you come to that, post up and we'll tell you how to use it.
As an aside, for jobs like this (which to most of us is relatively simple), you might want to consider a set of Do-It-Yourself books from Time/Life or Reader's Digest or something. These types of DIY jobs are definitely written into these books. (You missed Father's Day. Is your birthday coming? How 'bout an early Christmas present??!)