Unuasual Armpit Bruise

I am an obese 43 year old male who started a diet 1 week ago. Last year I was hospitalize for a week while doctors worked together to try to figure out my odd symptoms. Then, 2 bruises appeared on my upper thighs, almost identical. The bruises looked like a 2" thick lines about 6 inches long, almost as though I was hit across the legs with a baseball bat. They were red in color painful. A couple days past and it got brighter and bigger and more painful, and I began to feel weak with much difficulty breathing. Long story short with the hospital stay, I had developed blood clots in my legs, neck and lungs while in the hospital, doctors inserted a filter near my heart to prevent future clots and put me on Warafin for 13 months. They said the leg bruises had nothing to do with the clots, that is was cellulitis, and the clots were from an old injury I had to my shins years before. Bloodwork confirmed that.  
Just three days ago, 18 months after my hospital stay, I have mysteriously developed matching black and blue bruises under both of my arm pits. I wouldn't say it hurts, just that I can feel an annoyance there. The bruises are right at the fold of my pits in an almost perfect oval. I feel fine, actually good now that I have already lost about 15 pounds. Should I be concerned this may be the beginning of another blot clot episode, even with my filter in place? Or could it be something else?

[AllergyPA]

Those bruises could be infections, and you could have diabetes.
I strongly urge  you to  see your doctor.
I salute you for starting a weight loss program and wish you success.  Let your doctor know you are on a weight loss program.  He may want to see you periodically to ensure you are losing weight and exercising safely.