Both sides of my back bumper are sagging down because of rust on the rear fender, when im driving fast i can see the bumper moving around from my side mirror,what should i do abou this and any other rust spots that i have?

 

???

 

Seriously, other than ***-rigging it the only thing you can do is fix your quarter panels. Im guessing the most rearward portion of your quarter/wheel well is rusted out and the nylon nut that attaches the 2 sides is pretty much shot. If you dont want to spend money try some zip ties or patching your quarter if you have any auto body experiance.