Babies of this age usually do not shiver as they do not have shivering mechanisms.
If his lower lip or legs are noticed to have such movements, its quite likely that your baby may be having convulsions. Please do not panic but its important to be absolutely sure and safe in babies. You can get his blood tests done for calcium, sodium and potassium along with blood sugar. Also rule out any underlying infection by checking his blood profile. Breast milk contains very less amount of calcium compared to formula milk and many doctors give calcium supplements
for this reason. Colimex is given to relieve abdominal pain
but if the condition of your baby does not improve inspite of calcium and colimex drops, you need to review him with your Pediatrician
at the earliest.