1- Teething: he may be irritated because of the dental eruption process; if you notice that his gums are swollen and reddish/whitish over a particular spot, this is a sign of impending tooth eruption. Rubbing that spot with some paracetamol for infants on a sterile gauze may provide some relief.

2- New body movements: as you have mentioned, your baby has started crawling. This is a very new and exciting stage for him - before he was only sitting or lying down, moving only his limb but not his entire body from one location to another. To be able to crawl and eventually walk, he is acquiring new motor skills, and sometimes babies unconsciously do these movements during their sleep, which causes them to wake up startled. The good thing is that this is only transient.