Can a multivitamin, calcium and iron supplement all be taken together?

Vitamins: Yes, you can but there will be interactions. This is one of the issues with multivitamin and mineral preparations and why getting your nutrients from regular food is best. Just one example of interactions: all minerals with a chemical 'double plus' like calcium, iron, magnesium, zinc and copper get absorbed through the same channel and same area of the small intestine. Absorption of one will block.

Multivit: A good quality multivitamin is a good idea. You would need to get tested to determine if you rally need calcium or iron. Calcium by itself is not good, it needs co-factors like d, k, etc. To work properly. Most non-menstruating people do not need iron. Get a multivit w/out iron and if tests say you need iron you can supplement with it. Peace and good health.