I just want to second and third the idea that's been given here about the antibiotics causing the lethargy, fatigue, depressed feeling.
After years of scrupulously avoiding pharmaceuticals, this year I had to take antibiotics on two occasions. Both were potentially life-threatening situations, the kind that antibiotics are best designed to treat.
I experienced that dead, low feeling during and after both rounds, even though I did probiotics. The thing that helped me afterward was being careful to avoid all sugar, and to keep up the probiotics. I drank dandelion tea, a couple of large cups per day, and took 200 mg of Sam-e per day. Sam-e is not only good for mood, but is a powerful liver cleanser. In Chinese medicine, so much of what we westerners call depression emanates from qualities in the liver. I'm no expert, but the angry kind of depression marked by agitation, anger, and irritability is liver-connected, and I believe the low mood, lethargic kind of depression is also often a liver condition. Of course, in TCM they treat the whole system, not just liver stuck qualities in isolation. But either way, I think Sam-e is helpful. It's an antidepressant with many studies showing it to be as effective as pharmaceutical ADs, but is faster acting and without the side effects.
Depression can present in a number of ways: a lethargy so profound one can't move; an irritability that extends to skin and hair feeling like sandpaper, and many other symptoms. I think the various ways depression manifests indicate which neurotransmitter is out of balance. When my serotonin is low, I feel lethargic and sad, and SAM-e is great for that. When my acetylcholine is deficient, lecithin helps a lot. When my dopamine is low, I eat red meat (sorry, vegetarians!) to boost dopa. I do this kind of by feel. There's certainly no blood test level of science to how I evaluate myself.
I will add that Sam-e, being as powerful as Prozac, needs to be handled with the same care and respect as a pharmaceutical. Going off of it rapidly, or taking it haphazardly, can cause problems for some people. Just because it's OTC doesn't mean it's not extremely powerful. Once on Sam-e, I think one would need to be carefully weaned off it, just as one would with SSRIs.
The depression that followed my use of antibiotics was helped by the Sam-e and probiotics and dandelion and other liver-supportive herbs. If you think about how hard your liver has to work to handle the level of antibiotics in a Lyme regime, you can figure how much liver support you'd need afterward to spring back to life.
Good luck with it. And just my opinion, but I'd avoid pharmaceutical antidepressants unless you were experiencing a major, life threatening depression and in need of help. I've had friends who experienced major problems while on them. True, I've had others do well with them. I've not heard of anyone, however, who had a bad time with Sam-e.