Bruises are typically described as having a slight yellow phase and then the more classic black/blue discoloration that results from the leakage of blood cells from capillaries into the surrounding skin. Bruises do not typically become red, and as such the lesion on your lower leg is probably not the result of a bruise
A but bite can appear red and swollen, but these are typically described as itchy and usually subside within a week or two. Another cause of a red nodule that typically appears on the shin is something called erythema nodosum. Classically these lesions are raised and painful, and can be idiopathic (i.e., no cause is obvious) or the result of a medication (such as oral contraceptives) or recent infection (classically a Streptococcal infection). In other instances, erythema nodosum can be caused by an underlying inflammatory disorder, such as sarcoidosis or inflammatory bowel disease.
As the cause of your leg lesion is not evident and does not seem to be resolving, it is advised that you consult with your primary care doctor
to get an accurate diagnosis.