Thank you for your query on Healthcare Magic.
Your child seems to have gastrocoloic relux due to which she is getting upset and stiffening her body.
I advise you to do the following :
Burp after each feeding
Hold the baby in upright position for 10 to 15 minutes after feeding
Give small quantity feeds more frequently.
And nothin to worry as she is gaining adequate weight and thriving normally.
Still you are facing problem, consult your Pediatrician
for the advise.
Hope I have answered your query.