Help is needed

About twelve years ago I purchased a small Meyer Lemon Tree and a small tangerine tree. I planted them close to each other. Both trees produced really good fruit. This year I definitely have a problem with both fully matured trees. The trees started producing fruit but the fruit wasn't like a tangerine or lemon at all. Both trees produced fruit that looked like a huge lemon. I picked one off of the tree to taste it. The fruit wasn't sweet at all and the inside looked like a grapefruit. The taste was sour and it tasted like a grapefruit. I just want my lemons and tangerines back to normal. Can anybody suggest something I could do to get my lemons and tangerines back to normal.