Not receiving emails properly and sent messages not appearing in sent folder.

I haven't changed anything or clicked anything different but from Friday I haven't been receiving any emails to my inbox and the occasional junk email message. 

I have had my sister send me messages that haven't come through and she says are bouncing back. 

Also if I send a message, if goes as if its been sent but doesn't appear in the sent folder!?

Help!?

I need access to my email at all times!