Question about loosing to fast

Marley112586

My starting weight was 245. Im 5'9.5" 25 yr old female. I have lost 40 since mid October. At first it was coming off about 2 lbs a week give or take. But since I've started going to the gym it was been falling off. Last week I dropped almost 5 and so far I've lost 3 this week(my weigh in isnt til Friday but I was worried about it so I weighed). I burn 200-300 calories on the cardio machines then I do some strength training for about 20-30 minutes 4-5x's a week. Im eating around 1400-1500 calories a day. Should I be worried or is this normal? I just don't want any muscle loss and I want it to stay off for good!