Span, are you married to my DH??
I am also OD, every month, DH has no idea how bad it is, and would flip if he did. He also helped me clear mine once a few years ago but it has crept back, following birth of DS/maternity leave. I also pay for most DS stuff.
My stance is that if he has savings, which I know he does, and he isn't honest with me about his finances, I have every right to keep mine from him too. I know this isn't healthy, but my DH is also exceptionally tight and would watch every penny I spent out of a joint account. We differ in our approach to money, and that's ok.
If you need to clear 1800 in 3 months I would suggest you sell anything you can on ebay, live extremely frugally for 3 months, and possibly approach a close family member who might be able to help tide you over and you could pay them back rather than your DH?
I know lots of people here will be amazed by my response to your post but I truly understand where you are coming from, and would also do anything to avoid DH knowing my situation.
Either come totally clean and ask for joint account, or watch your every penny for a few months. You'll be amazed how it racks up.