Can fatigue/tiredness be a side effect of antibiotics? Dr. Rx'd Doxycycline 100mg 2x/day for 7 days for resp infection. Have felt more tired on it.

Yes - SEs of doxy. Doxycycline CAN cause fatigue, although usually this is less than 1% incidence. I would want to know also if you have any yellowing of the eyes or other symptoms... You should let the prescribing doctor know about this-sometimes they need to check blood work to make sure it is nothing serious (like a liver problem, or a blood problem like anemia). It's always good to be proactive about your health.