hi , i would have a really good look at the bit as my horse was the same and i didnt think there was anything on it until i had a really good look and there was little bugs on it and as soon as i cleaned them of she was fine again x hope this helps

Yes stick your thumb in the corner of the horses mouth this always seems to work.

You could try covering your bit in something sweet like honey or treacle which should work or you could try putting your finger in the corner of his mouth which then should make him open his mouth for you if they don't work then you should maybe try getting his teeth and mouth checked out

hope i helped

Pony Mad123 x