One of the primary drugs to treat giardia is Flagyl. Flagyl is one of the antibiotics that is notorious for inducing yeast overgrowth. If you now have yeast overgrowth, then you are being exposed to a yeast product called acetaldehyde. This product will interfere with your disposal of alcohol. It will also interfere with your methyl-folate and your formation of an active form of B6 called P5P. Without these two vitamin forms, your body is going to have a difficult time creating your neurotransmitters like serotonin, dopamine and epinephrine.The yeast product will also cause you to lose your taurine, NAD and your alpha ketoglutarate. All of this may contribute to sleep problems. I would guess your new intolerance to alcohol and its effect on your sleep is caused by an overgrowth of yeast and a struggling liver. Fortunately, there are things you can do about this.
Pantethine and molybdenum will aid the removal of alcohol and acetaldehyde. The pantethine will also help heal your liver. (Note this is pantethine, not pantethenic acid or pantothenate. They are related, but not quite the same thing.) Pantethine may cause diarrhea or cramping if you get too much. So start with one pill per day, taken with a meal, and see how your body tolerates it before increasing the dose.
Another thing that is required for the removal of alcohol and acetaldehyde is NAD, which is a form of niacin. Take the NAD under the tongue and let it dissolve. Too much of this might cause constipation. However, a modest amount should be fine.
Sometimes supplements of pyridoxal-5-phosphate will help with sleep. Initially it may cause some aggitation as your body adjusts to having it again. Therefore, I suggest that you start by taking it in the morning. Later, you may notice that it doesn’t matter when you take it. I happen to like Country Life’s product called Active Coenzyme B6 because it contains both P5P and PAK.
Taurine may be of some benefit with sleep, too. However, I’d start it also in the morning. Also start very slowly with taurine, as it will release some toxins from cells, and you don’t want to overwhelm an already struggling liver.
Alpha ketoglutarate may be low because of the yeast and alcohol. Among other things, alpha ktoglutarate helps the body remove ammonia. Too much ammonia will cause sleep disturbances. The alpha ketoglutarate is something you want to start using in the morning. Just like the P5P, there may be an initial adjustment period. Also, the alpha ketoglutarate might cause constipation. You may want to play with a balance between pantethine and the alpha ketoglutarate if you have trouble with diarrhea or constipation.
Just curious. Did they tell you to not take alcohol while you were using the Flagyl? (Flagyl interferes with the removal of alcohol from the body.) 
1.Gupta NK, Woodley CL, Fried R. Effect of metronidazole on liver alcohol dehydrogenase. Biochem Pharmacol 1970 Oct;19(10):2805-8.