Calories, BMR, noob questions (I'm STILL waiting on my book!)

I hope these aren't covered in the book; my book is still somewhere in USPS land, and I didn't want to hijack someone elses post.
I am 30 years old, female, 5'6", 157 pounds. I do defensive kickboxing two hours a week (T/Th) and ride horses on the weekends (it's not really strenous excercise, but definitely work). The rest of my time is spent at a desk (accounting) or laundry/housework. I half-ass IF each day from dinner (6-7pm) to lunch (11 am) with the exception of coffee and heavy cream so that I can take my drugs. Maybe that ruins any benefit I'd see?
I have checked varying places to determine what my base caloric need is, so that I can figure in a 4-500 cal deficit, and hopefully start losing some fat, but I have no bloody idea what I need.
I've done two rounds of HCG, which did nothing for me, and I'm afraid perhaps it 'broke' my metabolism, which was already faulty thanks to a malfunctioning pituitary gland. I don't make TSH, which means my thyroid must be completely endogenous, and I take 6 1/2 grains Thiroyd (NTH) per day. My basal body temp is high normal, but I have no other signs of hyper. I also take 6 mgs of methylprednisolone to replace what my adrenals glands do not make; a physiological rather than pharmocological dosing. No idea if it's pertinent or not. As a teen I did have EDNOS-a combination of bulimic and anoretic behavior, but once I got my adrenals fixed, that behavior vanished.
My caloric intake ranges from 12-1800 a day, but I haven't seen a single pound of weight loss. My carbs have been consistently under 50, usually closer to 30; my protein is roughly 90 - 115, based on an estimated LBW of 108, and fat makes up the difference. (Per sparkpeople.com)
I don't sprint, but I do 'rapidfire' - jabs/hooks/roundhouse in sets of 20 to thirty seconds for what ends up being nonstop for anywhere from a minute to three, pushups and situps to failure twice-beginning of class, and again and the end. Same effects as a sprint, I think-maybe I'm wrong and need to add that in on top? By the time we're done with our sets, I'm blowing hard and its all I can do to finish.
Is there a reliable way of determining caloric need other than cutting back til you start losing? I'm afraid of cutting calories TOO far, and further slowing my metabolism, but I'd really like to be rid of my baby weight. He's going to be four in Oct, so its not been a good excuse for oh, three years now!
Thanks!
Laurel
Last edited by Eklecktika; 06-30-2010 at 01:17 PM.
Chief cook & bottle washer for one kid, a dog, 6 hens, 2 surprise! roosters, two horses, and a random 'herd' of quail.
~The ultimate ignorance is the rejection of something one knows nothing about and refuses to investigate~