1998 Chevy Malibu sweet smell from exhaust

Engine problem
1998 Chevy Malibu Engine Size unknown Wheel Drive Type unknown Automatic 128, 00 miles

Hi there. Let me give you a brief history.

I needed a new serpentine belt. I brought it in and they did a complete diagnostic on my '98 Chevy malibu. They recommended that the lower intake gasket get replaced (now I have learned that this seems common with malibus) b/c it was leaking antifreeze. I then had that fixed for about $800.00

Then yesterday, when I got home, I smelled a sweet smell coming from the exhaust pipe. From what I'm reading on the internet, it seems to be an antifreeze problem again. What happened? Why does this problem keep happening? What's it going to cost to fix?

Thank you

Mary