I've been on Doxy for 3 weeks, 100 mg 2x a day. Then I started new symptoms in my knee, slight swelling, and the dr. switched me to ceftin. Been on it for 2 days, and today I had a bruise on my stomach, between my left hipbone and bellybutton, which is a weird place for a bruise. I've had a little tenderness on the left side of my abdomen area, maybe 6 inches around. I also have a tendency to take pills on an empty stomach. Is this strange or just a coincidence??? I've been watching to see if the bruise grows, but as of the end of today, not yet.