My initial impression is that this may be a situation of over training fatigue given the reduced calorie diet and the demands you are placing on your system.
It would be helpful to have an idea of what you are doing for weight training and cardio and on what schedule. Also, have you taken any breaks from lifting at all in recent months. A lot of trainers will recommend one week off of lifting every eight to ten weeks to give the body time to catch up on the demands you place on your system. A lot of people think that just because I don't have much soreness in the muscles means that I am fine. That isn't always the case, as lifting places significant demands on your not only your muscles, but also on your bones, connective tissues, nervous system, your immune system, as well as the endocrine (hormone) systems.
It's important when you are lifting to pay attention to your bodies messages. As much as I hate taking time off myself and I know how hard that can be, sometimes if you are feeling tired and worn down, the best thing to do for yourself is to take a few days to a week off of doing any lifting.
Now it may not be this either. It may be a dietary issue, just because you are eating 1800 cal. per day doesn't mean your getting enough vitamins and nutrients. Resistance training significantly increases the levels of many nutrients that you need. Are you taking a multivitamin and or any supplements? This would be helpful to know as well.
I have a suggestion for you that wont take much other then a little effort. Go to fitday.com (its free) and register an account. You can track everything you consume and all your activities there. Once you've done that for a week, go to the reports tab and run a nutrient report for the previous week, and this will show you how much of all the nutrients you are getting and if you are deficient in any of them. Keep in mind though that this tool doesn't consider that you may be needing more then the RDA of some nutrients. You can also look at calorie deficits for the day or week, or two weeks or month or whatever. This can give you an important idea of whether or not your diet is cutting to many calories for your activity levels.
I know this requires you actually doing some work, but please consider doing this. It's a free tool that can be invaluable in your quest to achieve the idea body. Free tools with this kind of value are rare, use it, not only now to help determine the cause of this tiredness, but also consider it as an ongoing tracking tool that gives you a lot of insight into how things are going for you in your efforts.
If you can answer a few of the questions about routine, breaks, nutrients, and vitamins/supplements, I might be able to help with some additional suggestions.