Fet with natural cycle

I’m doing a fet with natural cycle and I have a couple questions I’d anyone has done this.

Why did they give me a trigger ? (Ovidral). I ovulate regularly.

Can you still have sex during the cycle or did you doctors tell you to abstain and /or use protection?

What happens if they don’t do the trigger before you ovulate ?

How long after you ovulate do they do the transfer ?

Thanks!