Yum problems

when I try to use yum I get the following messages
Traceback (most recent call last):
File "/bin/yum", line 29, in <module>
yummain.user_main(sys.argv[1:], exit_code=True)
File "/usr/share/yum-cli/yummain.py", line 375, in user_main
errcode = main(args)
File "/usr/share/yum-cli/yummain.py", line 281, in main
return_code = base.doTransaction()
File "/usr/share/yum-cli/cli.py", line 817, in doTransaction
resultobject = self.runTransaction(cb=cb)
File "/usr/lib/python2.7/site-packages/yum/__init__.py", line 1834, in runTransaction
lastdbv = self.history.last()
File "/usr/lib/python2.7/site-packages/yum/history.py", line 1271, in last
ret = self.old([], 1, complete_transactions_only)
File "/usr/lib/python2.7/site-packages/yum/history.py", line 1220, in old
executeSQL(cur, sql, params)
File "/usr/lib/python2.7/site-packages/yum/sqlutils.py", line 166, in executeSQLQmark
return cursor.execute(query)
sqlite3.DatabaseError: database disk image is malformed

rpm database is good tried all usual yum stuff clean all clean metadata etc but still have this problem?
Please can anyone help

Thanks in advance