Is a seaweed wrap body treatment safe while breastfeeding? I had one, if it is not, how long should I wait before breastfeeding again my 5 months old?

Yes. As long as a seaweed wrap is definitely as it states just sea weed than it should be safe with breastfeeding. With that said, I would recommend contacting the spa / salon just to make sure there weren't any other chemicals. Even in the event that there were chemicals on your skin, once washed off breast feeding should be fine but I would still recommend consulting with a lactation consultant.