Should I eat less now that I weight less to continue losing?

Currently I eat 1500 calories a day. My diet consists mainly of white meat, fish and vegetables. But don't worry the carbs are there too.
I lift 3 times a week and usually do about 20-25 mins on the elipical before these sessions. Usually on my gym days I eat more and it works out a 1500ish with cardio taken into account. On the days when I don't go to the gym I'll usually jog for 20 mins - half an hour burning between 200-300 calories. On these days I stick to my 1500 limit.

My goal is to lose fat. And that is certainly what's happening. But now that I've lost a stone I'm wondering if I should reduce my calorific intake in order to continue to achieve fat loss? I read this yesterday in a body building forum, but I'm just a regular joe and wonder if this applies to me? (I am female, 22, weighing 134.6lbs with a goal weight of 126)

Yesterday I consumed 1400 cals, and went to the gym this morning and could barely do my sets. I was very disappointed and believe this could be down to not eating enough. Should I stick with 1500? So far it has worked for me. However the last few weeks my weight loss has been impressive losing 2lbs sometimes more a week. I didn't think this was possible considering my starting weight was not particularly heavy and had aimed at losing 1lb a week. But now the rate of my weight loss has slowed down to this.

I eat 3 meals a day with plenty of snacks and reasonable sized portions. Although I find i'm constantly eating and always satisfied my stomach seems to be shrinking and I can't eat as much. There have been days where at the end of the day i've consumed only 1000 calories although feeling full and eating a balanced diet. When ever I see the little "you are not eating enough calories" in red at the bottom of the screen on mfp it makes me feel guilty! What should I do??