chilis can have 2 or 3 growth periods in the year. Maybe yours is just about to start again (give it a feed)
if it really does look poor, probably best to take the fruit off and give it an extra chance. It you try one of them and they aren't hot and they were supposed to be, maybe leave them on a bit longer
they won't turn red off the plant probably but that doesn't matter
chilis freeze very well by the way.