Welcome.
Depends where you've been. Have you been within 200 klicks or so of the English coast? If so, you should have seen aircraft, as long as you're not running in high TC, which tends to result in missing them. Have a look at the convoy route map which also shows air cover. Air coverage roughly pre-41 is quite limited in range.
edit/add: And obviously if you have bad weather, that will cut down on sightings.