Am I eating enough calories?

I JUST started counting my calories - I suspect I was eating about 2400 before. I'm 5'8 and 148 pounds. 21 years old. Trying to lose about 10 pounds.

I just seem to be having a hard time getting the balance right in the middle, not too many, not too few.

I usually exercise, burning about 400 calories, 3 times a week, and I lift weights 3 times a week. I also walk quite a bit, a total of about 2 hours a week.

I'm too busy to exercise this week though.

Day 1 - 1490 (burned 100 at the gym)

Day 2 - 1208

Day 3 - 1197

Day 4 - 1221

Today - probably 1050 max by the end of the day (around 900 right now and it's late)

My guess was 1200-1300/day. Does that sound right? Am I eating enough given I didn't work out? What about if I WAS working out?

Thanks!