There may be several reasons for the "crash" you are experiencing, but the main thing to remember is that the mouth and body are connected. Generally people do not realize the oral-systemic connection, but it is real. Depending upon how long you had the infection, yes, your body may still be trying to recover. Were you on antibiotics and if so for how long? This may have disrupted your gut bacteria which is a primary player in the immune system. It is important to get not only that gut bacteria back into balance but also your immune system. This can be done through proper nutrition and possibly the addition of a probiotic. If you are still feeling down after 3 weeks total, I would consult with your MD to be sure there is not an underlying medical issue. If nothing is found to be medically wrong, I would seek out a professional nutrition experience (this could be a dentist, functional medicine doctor, naturopath and the list goes on). I hope this helps.