In regards to unlevel areas: Is the home on a crawl space or slab? Older homes have a tendency to shift a little with age and the local terrain. If it is on a crawl space and has significant dips, you may have some bad subflooring. You may have to contact a contractor or structural engineer to determine the reason for the sinking.
If the sellers agreed to correct problems before closing and they did not, you should entertain this issue with and attorney to resolve or make this seller perform the duties they agreed to.
If there were problems in the home inspection you should have submitted a request for repairs in writing and received a signed copy from the seller agreeing to the repairs. At the walk through you have to satisfy yourself that the problems have been rectified. Most people want invoices from licensed contractors for repairs made as a result of an inspection. At the walk through, if you were aware of problems that still existed and still closed, you probably lost your recourse.
As far as sinking or unlevelness this could not be just occurring it must have been known by the previous owners.