You probably just need to replace the battery. The normal way these
things work is that if you manually change the temperature setting (and
don't hit HOLD), it stays that way until the next programmed change. If
you manually change and then press HOLD, it stays that way
indefinitely. Pressing the reset button will reset the programming,
which might be set as a default to something like 60 during week days,
68 in the morning and evenings, 68 on weekend days. And it sounds like
that is what you are living with.

If your battery is dead, it probably forgets everything after 5 or 10
minutes, including your manual change. Since you have been struggling
with this for 4 years (!!), I am guessing that your battery is at least
that old. It's usually just a single AA battery in the thermostat
itself.

-Kevin