If it is a calcium allergy, it must be localized to your digestive system. Otherwise, your body would be rejecting your bones and teeth and your nervous system would shut down because calcium ions are part of the mechanism for transmitting neural impulses. Do any of the diarrhea or gastric upset medications help when you ingest calcium? Vitamin D will help your body make use of what calcium it does get. Maybe you could take an osteoporosis medication like Boniva.