Mums not letting me out even though she said I can before?

Okay so I’m supposed to go out with my boyfriend today and I asked my mum a few days ago and she just nodded so I took it as a yes and now as I’m about to go, she says I can’t go. This is like the 4th time I don’t want to upset him cause he gets upset by this. What do I do? I think its because me and my mum have had our ups and downs when social services got involved she’s started to be like this