too much working out?

I have been working out with cardio doing step aerobics or body attack(running,jump squats,plyometrics,etc.) and I do this for 6 hours per week.  I have been working with a trainer doing weights for 3 hours per week.  I am 5'7'' and weigh 175 and would like to weigh 145.  I am eating 1600 calories per day with 1 cheat meal per week. I have only lost 1 pound in 4-5 weeks.  Am I working out too much with cardio or what am I doing wrong?  Please help!!!

It's possible that you are losing fat and gaining muscle. However, 1600 calories is probably not enough given all the exercise you are doing. My suggestion would be to increase your daily calories by about 400 - 500 per day and see how it goes for a bit. Right now, your net calories per day are probably way below 1200, which means you're body could be in starvation mode.

You're averaging 1.25 hours per day of moderate to vigorous exercise. Even assuming you're not pushing it at 600 kcal/hr, you're still burning 750 kcal/day. Further assuming your basal metabolic rate is 1800, your caloric deficit is 950. Try eating a little more or working out a little less. I'd decrease cardio before weights (3 hr/week doesn't sound extreme, as long as you're not doing powerlifts). Also, are you getting sufficient protein? I've heard recommendations between 0.8 and 2.0 g protein per kg of body weight; this suggests that you should be getting at least 64 g protein per day. Any less might enhance the starvation response.

I've been aiming for a net deficit of 500 kcal/day below my calculated BMR plus whatever I burn (e.g. my BMR is 2500, today I burned about 400 at lunch, so I'm going to eat 2500 + 400 - 500 = 2400 total), and so far I've been losing weight and still able to run/swim/bike without feeling totally weak. If today's deficit is around 1000, I'll bonk during tomorrow's run.

eat more. dont work out less. you need to consume at least 2000 cals working out as much as you do.

How do you calculate my bmr? 

In the "Tool" section at the top of the page is a form to fill out to get your bmr.

so what is wrong with a 900 cals deficit?