Hi Andrew
There are many factors which determine how frequently a monitor may visit your site. The latest developments suggest that a risk assessment be undertaken and a monitoring plan drawn up by the sponsor. This will document who gets visited and when. If you are doing a low risk study perhaps on a marketed medicine within its marketing authorisation --- nowadays termed Type A -- and are contributing few subjects to the trial it is likely that you are low priority for a visit. That said the sponsor should not ignore your activity and should at least visit in the early stages of the trial to check that things are going ok. If you are conducting a trial on an unlicensed investigational medicinal product you are likely to be visited more frequently. If you have not had any monitor visits then you should make extra effort to make contact with the sponsor to discuss that as they do have oversight responsibilities. You should have been given contact details.
Hope that helps.
David