Do your neighbours with Freeview all have large aerials ?
If not, it might be that you have either an aerial made for the wrong group, faulty aerial downlead or patch lead or faulty/insensitive Freeview box or IDTV.
Check via the Wolfblane website, entering your postcode, to see what is recommended.
Then report back if necessary.
You can read many similar threads in this forum to get an idea of the process.