Infantino carrier is killing my back - when to side carry?

My dude is 18lb. I don't know the weight limit for front carrying, but my back says 18lb. Do I need to wait until he can sit up on his own to transition to side carrying?

Edit: I found one on sale that may work for me. Really good reviews on back support specifically. :) I can't afford an ergo or Tula at the moment, but the Yokohama sounds promising. I'll update in a few days here and on r/babywearing with my experience/review and if it's worth it to me.