I hope somebody can help!

I've had my Sensation just over a week, and for the first few days everything seemed to sync fine. I use Gmail, and also have my Google Contacts and Calendar synced. I was getting regular notifications as soon as an email came through.

However, the last 3 or 4 days I haven't had a single notification. I thought this was weird as I know emails are coming in, but I have to go into the Gmail application and press refresh (or go into Accounts and Sync and do it from there), before anything comes through. I have checked under the "Accounts and Sync" that everything is still checked (which it is), but notice that there must be huge periods of time between syncs. It is currently 17:40 and I've just looked and the last sync, for Gmail, Contacts and Calendar, was 10:45, nearly 7 hours ago!!!
After a bit of troubleshooting (finding other people with similar problems), I have tried a few things but to no avail - I noticed someone suggested setting up Gmail in the "Mail" account and just turning off the Mail notifications, but this has made no difference. I also found people suggest clearing cache and data. I have cleared cache, but not cleared data as I get a warning message and don't know if I'm doing the right thing! Maybe this is the key, but I'm not sure!

Anyway, I can't see any reason for it to just have stopped fetching mail automatically, and it has nothing to do with my wi-fi or mobile network signal, as I can be sat at home all day with a full wi-fi signal and it makes no difference. I would be happy if I could just get it to sync every hour or something, but there seems to be no update schedule option for the 3 Google apps. I know Gmail is supposed to fetch mail as soon as it comes in (although mine has obviously stopped doing this!), but don't really understand how not having a "sync schedule" (one that you can adjust at least), works for Calendar and Contacts.

Does anybody have any bright ideas?

Thanks