3 yo pooing once a week

[kennycat]

As delightful sounding title suggests really! My son is fine with weeing in the correct place (prefers potty to loo but I'm sure he'll get there) but still has several accidents of a poo kind. Sometimes he gets to the potty or loo, mostly not though. It is not uncommon for him to go a week between poos and I don't know if this is the problem - it's like he just doesn't get the practise of having the feeling of needing to go often enough for it to be a habit yet. I'm tearing my hair out and he must be sick of hearing me ask if he needs a poo every time he crouches down with his bum in the air.

Any ideas please? He starts school in September and I really want this nailed by then.