Does baby being fussy while breastfeeding could mean growth spurts? Tried (my sister) switching boobs and position and dun think bec of gas but still baby won't stop crying and like throwing his whole body out of anger.

There are lots of reasons why baby could be crying --- here's a helpful article: https://ph.theasianparent.com/reasons-why-babies-cry-after-breastfeeding-2/ For my daughter though, that level of inconsolable crying (throwing whole body in anger) was usually gas.

How old is the baby? Growth spurts occur at certain points of a baby's life, and it may happen only once in a while but not always. Try to familiarize the baby's cues.