What does it mean when you wake up with random bruises on my legs?

Many reasons: May be bug bite, may be medication related, may be due to a blood problem that is causing easy bruising, it could also be due to a connective tissue problem i.e. A skin problem that increases easy bruising. From your description does not appear to be allergic reaction but a health professional may need to look at it. You need to show it to your doctor if it keeps happening.

Many things: Bruising occurs when there is excess leakage of blood under the skin from broken blood vessels. Therefore problems such as fragile skin/blood vessels (due to steroid use), problems with ability to stop bleeding (low platelets, vitamin k deficiency, hereditary or acquired clotting factor deficiencies) can cause symptoms such as yours. Please see your physician for further evaluation and referral.