Hello people - I've been taking Doxycycline for about 4 weeks now (for Chronis Prostates) and started experiencing aching in my muscles, mainly my legs (back of thigh, calf and behind the knee mostly) about 2 weeks back. It started very subtle and has got stronger each day. I don't know if this is a side effect of the Doxycycline or just some lovely new medical problem I'm developing - but I thought I should post up my experience in case anyone finds themselves in my position and they too want to know if anyone else has got worsening aching legs whilst taking a long course of this medicine. I'm going to speak to my doctor about this tomorrow and stop taking the drug. I'll update you all with another postas to how things develop. Hope you all get well folks!