Itching is one of the most common complaints in dermatology practice and there can be hundreds of reasons for it. As you have mentioned you recently delivered, it doesn't convey how recent as it could be due to one of the drugs used during the delivery. It can be bacterial fungal viral infection or parasite infestation. It can also be a component of a precipitated auto immune disease post pregnancy. The pimples on the chest can be a part of acne as you rightly suggested. But apart from that it can also be as a part of Seborrhic Dermatitis, or pityrosporum folliculitis or bacterial folliculitis. Kindly get it examined and assessed by a qualified dermatologist in person for a proper and thorough evaluation. Hope this was helpful.