Weird smelling water

Hi, My boyfriend and I just recently purchased a house that has well water. The property had sat abandoned for a few years so the water softener system and hot water tank needed to be replaced. It took a few weeks to get the water softener system hooked up, so we used hard water in the house for a few weeks. During that time, we noticed an eggy/iron type smell from the water, especially the hot water. When we first installed the softener system the smell went away, but within the last week or so it has come back full force. Does anyone know what the cause might be and how to fix it? Thanks!