Exercising, watching calories and...nothing.

I am 35, female and weigh 197. I started regular excerise last October starting at 227 working out to aerobic DVDs. In Jan, I got another set of DVDs that incorporated some weights as well. I lost 27lbs. by Feb. then nothing. I continued with exercise (about 5 days a week - aerobic and dog walking when the weather is nice) not worrying about weight loss or lack of. By May, my frustration grew when there was no movement on the scale so I got another set of DVDs to change the routine and lost 2lbs. It is now Aug. and I feel my aerobic exercise is high (200+ min. a week; 6 days a week) and my calorie intake is good 1500-1800 per day. I track everything I eat including any junk foods but I don't over do when I have them. I understand calories in and calories out so I must be in balance and therefore no weight loss is occurring but I'm exercising as much as I can and on some days I feel like I can't get through the routine and I feel tired while doing it which isn't the norm. I sleep like a rock for 9 hrs and I have energy through the day. I know I have areas to work on such as getting more veggies and water but I haven't been watching the amount of fat, carbs or protein. I have incorporated some protein bars into my diet because I've added doing bicep curls in the evening a few nights a week. But I'm not doing any serious weight training. I'm just wondering what I'm doing wrong? I'm exercising more now and at a stronger intensity than when I was loosing weight and nothing's happening. I've only lost 2lbs since March and I don't want to stop exercising for fear of getting out of the habit but I feel like I'm running in circles very fast :). I've lost weight before (30lbs) when I started college but I was living off of cheeze-its and animals crackers and walking for 8 hrs a day but that's not healthy and I gained the weight back +30 so I don't want to go that route. I've tried weight watchers point system and nothing happened there either but that was with zero to little exercise. Any comments or suggestions would be appreciated to help me kick start the weight loss again.Thanks!