L.D.
My son has sensory processing disorder. What really helped for us was having him work with an occupational therapist who specializes in sensory processing disorder. Also, reading the books The Out of Sync Child and The Out of Sync Child Has Fun are a definite must. My son was probably about 4 when we started with the private OT and he did treat with the OT for about 2 years for this issue alone. Most of the issues that we were dealing with at the start (mouth undersensitized so that he was packing food on the roof of his mouth or constantly putting inedible objects in his mouth to sensory seek, head overly sensitive, poor body awareness, obsessively needing sensory input from other people's eyebrows) have all pretty much been worked through and are mostly history by now. He still gags at the smell of bananas and lunch meat but, in the grand scheme of things, we can pretty much live with that.
I hope this helps. If you give your son the supports that he needs, you will definitely see some vast improvement and this doesn't have to be a lifelong imposition. And just remember that what you are seeing with your son now is just a brief snapshot in time in his life. I've found that it is really helps to keep this perspective.
Blessings.