(My answer is a collection of advice for sleep, not for the hives)
I would take 5HTP instead, as it converts to serotonin and then melatonin. The serotonin, if not in balance, will elevate and make you feel de-stressed. The melatonin is a neurotransmitter that your brain needs in certain balanced amounts, and I like to let the serotonin turn into that naturally by taking 5HTP so that it has it in balanced amounts.
If you are fatigued all day but wake up at night (after 6:00) it is one of many signs of adrenal fatigue. I would see if you had the other signs and symptoms and then work to balance it out, perhaps by buying a good adrenal complex formula.
Make sure you turn out/dim your lights when it starts to get dark out. This tells your brain/hormones to start producing melatonin and to get ready for sleep. If the lights are on, your hormones think it's mid day and try to keep you powering through it. I completely covered up my bedroom windows so that streetlights don't pour through. It's so dark you can't see you hands in front of your face. I bought a nightlight for the washroom that is so dim it is like moonlight.
Don't work out at night, and don't consume any coffee or stimulants after 4:00. I can't sleep because of stress sometimes, and I take some GABA, which is actually a neurotransmitter, but I take it in small amounts and it calms me right down. l-tyrosine helps with emotional and psychological stress, and I take that sometimes too. I also take magnesium (actually, it's a good quality cal-mag by inno-vite) before bed which relaxes the muscles. Then I just close my eyes and try to fall asleep, I think of lying on the beach and listening to the shore at night. I imagine that it is pitch black and I just kind of drift to sleep. Sometimes I just imagine a white, lit candle, the flame undisturbed by the air. Or, you can count breaths, or instead of counting, think of which breath it is "in... out," and sometimes I just do some relaxing deep breathing... these ensure that you relax and you don't start thinking of what you have to do tomorrow and all that stressful stuff.
There are other things you can take to wind down before bed, like passionflower or valerian root. There are lots of complexes you can buy in the health food store that combine herbs, amino acids and minerals to relax your body and mind for sleep. Everybody is different, so keep changing it up to see what works. I actually tried a homeopathic one called "insomnia" and I found I fell asleep eventually, but it gave me some really crazy dreams (not in a bad way).