Tanuja,

     Rashes on infants are very common and, as you've proven, not necessarily induced by changes in diet; however, you could consider the baby's environmental changes. Is it safe to assume that you travel often with your baby? The climate in Bangalore may be generally different than in Kerala, so maybe changing temperatures or humidity contributed to the skin reaction.  The constant shift in climate could be triggering the allergy, which is why I ask if travel is constant. If that's the case, it might be heat rash: http://www.mayoclinic.com/health/baby-rashes/FL00090&slide=5

It could also be eczema, which looks alot more like what you've described:

http://www.mayoclinic.com/health/baby-rashes/FL00090&slide=6

Another possibility is contact dermatitis which is basically skin inflammation after coming into contact with a new detergent, perfume, or fabric the infant might be allergic to. Perhaps the reoccurance of the rashes is due to something your child's skin regularly produces, such as sweat. Most of these conditions are treated with whatever antibiotics or topical ointments your doctor will prescribe, so I really hope that they figure out what it is exactly. I hope this information has helped you out at least a smidge :) Best of luck.