This is an older baby, about 3 or 4 months of age, whose mother’s production has decreased. See the information sheet Slow Weight Gain Following Early Good Weight Gain for some reasons this decrease in milk production might occur. Some of the reasons that may result in a decreased milk production include the mother's using a hormonal birth control method (including hormone releasing intrauterine devices or intravaginal hormone releasing rings), the mother's feeding one breast at a feeding "as a rule" instead of "finishing" one side and then offering the other. But the most common reason is the one discussed in the paragraph "This reason (number 11) requires more explanation".
The baby is jiggling and unsettled at the breast because the flow of milk is slow. Note that he hardly drinks at the breast (very few pauses, see the videos Really Good Drinking, and Good Drinking), though his chin is a little bit difficult to see.
This sort of behaviour is often said to be due to an over rapid milk flow but by watching the chin one can see that this behaviour in this case is due to too slow milk flow. However, babies pull at the breast more frequently because the flow of milk is slow rather than because the flow of milk is "too rapid".
Note that giving such babies bottles, may quickly result in their refusing to latch on.