K.S.
You have been getting some good advice from other posters. If trying a few things on your own doesn't seem to help, I would definitely look at info on sensory processing disorder. "The Out-of-Sync-Child" is a good book (it helped me a lot with my son) although in your situation I would recommend starting with a book called "The Highly Sensitive Child" by Dr. Elaine Aron. I haven't read it but it comes highly recommended. I wouldn't seek any assessment until you have done a little background so that you can advocate for your child and have a sense of what, if any, services might help. We had great luck with occupational therapy in the case of my son with sensory processing issues.
Good luck. I know there are people who will say not to worry and that everybody is different. But I think when a child's relationships are being so affected that it is worth helping where possible.