I presume your Avios are held in BA as you are posting on the BA forum.

When logged in to the BA website, under membership scroll down and there is a 'statements' section. In there you will see your current balance and all your activity.

Avios themselves don't really have an expiry date- unlike with some points schemes, you don't have to use them in a certain timeframe. But all your Avios are forfeit if you haven't had any activity in your account for 36 months. So you need to earn or spend at least 1 Avios in that period to keep them all alive.