I am new to this and my "boss" has been after me to lose weight or I won't have a job any longer.The "boss" has been booking the thinner escorts,and leaving me for the casual appointments which does not pay any bills.How do I get around this?

Hi and welcome Meena,
You might think it's a little daunting, but I would go independent. Being a BBW myself I know there's definitely a market for ladies that aren't a size 10-12. You don't have to be ultra slim to get work. But the problem with most agencies is that they're blinkered in their views and they don't think there's a market for bigger ladies. They probably may not even had a call for them, but it might be because they haven't marketed you properly. They don't think you'll get work, so they haven't bothered to market you properly.
I have to ask, why did they take you on their books in the first place?

If you still want to keep working for an agency, find one that caters to bigger women. There are specialist agencies out there that actually do cater for the bigger lady. It might be worth looking into that.