It would be interesting if you could meet a physician for a proper evaluation. Spontaneous bruises in the body usually arise form numerous medical conditions. Conditions like low platelet levels usually causes these bruises. However, even allergic reactions and other autoimmune conditions could also cause this. Irritations from insect bites
or certain bacterial infections could present themselves in a similar fashion.
But in your case, its more like to be either and allergic reaction to something. I advise you meet your primary care
physician for help.
Hope this helps and have a great day,