If you're feeling like tiny bugs are crawling on your body and no tiny bugs or any bugs are actually crawling on your skin then it could be because of a condition known as formication.
When people experience formication it causes a feeling of tiny bugs and other crawling sensations on the persons skin.
Formication can be caused by some conditions such as fibromyalgia and Parkinson's disease.
So it would best to get checked out by a doctor to make sure it's nothing serious.
There could also actually be tiny microscopic bugs that cannot be seen that could be crawling on your skin and sometimes taking a good shower and washing your back with some body wash and a back scrubber can help get rid of those unseen bugs.