My Twitter keeps sending out spam messages...?

[Mona Mayfair]

I keep finding my account has sent out spam tweets, something about "stay at home mum earns a billion quid per hour bla bla bla let us con you..."

I hate spam and people who just go on twitter to spam others really piss me off, so I'm kind of angry these messages keep being sent from my account and I can't figure out how to stop them. It's really just generally annoying and is probably irritating my followers too as I've had several unfollows since it started happening.

Yeah, any ideas how to make these message GTFO?
I never click on obvious spam links. I'm pretty good at spotting them and can't remember clicking on one, which is why I'm so confused as to why my account keeps posting this stuff.