MY Zone users

How often do you replace the strap? Not the module just the strap..
I feel like I start to get wonky results after a few months of use. I do not know if it is me analyzing too much over the 50-100 cals missing...or if the belt does need replacement that often. Starts to seem VERY difficult to be in the yellow and impossible for red even though I feel I am busting my tail. Max heart rate unchanged - work outs done on rotating schedule that starts to repeat at approx every 2.5 - 3 months.
( used 6 times per week - wash machine wash cold every so often otherwise rinsed well in sink with light antibacterial soap and good rinse and hung to dry and I use ultra sound gel every time )

Any insight would be helpful and appreciated ~