Question
Is it ok to place a piece of plywood under the matress to help for the back pain?

Answer
Gloria,

Thanks for the question.  You have to understand that placing plywood under your mattress is going to make the mattress firmer, or harder.  That does not necessarily mean that the mattress is going to give more support.  It also doesn't mean that it is going to help relieve back pain.

If your mattress is very old and you sink into it, you simply need a new mattress.  Plywood will likely not help and it would be more efficient to put the $15 that you will spend on the sheet of plywood toward a new mattress.  

Also, if you are having back pain that has been present for some period of time and is not going away, you need to seek the opinion of a qualified doctor.  Whether it be a chiropractor, osteopath or medical doctor, someone needs to make sure that there is nothing significantly wrong with your back.  Pain is the body's way of telling us something is not right.  Get it checked out and let the doctor tell you if you need a new mattress or not.

God Bless,

Dr. Boss