Turn off automatic updates. Sounds like an update is failing to install and is being retried every time you switch on. If you can identify which one/s are responsible you can tell the update to ignore those specific updates.
Like grey george says turn off automatic updates and try and download them manually one at a time. If it still does not download click on each of them and a box should open up underneath just a matter of ticking the box for do not show update again. Not a fix but stops them trying to download all of the time.