I have a bruise. i don't know how i got it, but i've had it for more than a month and it still hasn't healed. could it be melanoma?

Probably not: Bruise is from some trauma or pressure injury and rupture of capillaries. It fades definitely in month. If there is a new skin discoloration of 1 month duration not itchy, rapidly spreading in size get it checked with your doctor. If same size with clear outline= may continue to monitor for 6 months. If there is family History of skin cancer and especially Melanoma yes get it checked.

Need more details: Your description of the skin change as a bruise needs more input from you. Perhaps you could take a photo with a cell phone and email it or give a better description. How big is this--please provide measurements. What is the color, has it changed in color or size since you first noted it, where is it located, does it itch, does it bleed, was there a definite history of trauma to the area?

Bruise: A bruise can take several weeks to heal. It should fade and change colors as the blood is reabsorbed. If this lesion persists or becomes worse you should should it to your friendly dermatologist. And remember to protect your skin. Wear a sunscreen with an SPF of 30 or higher and try to cover up as much as possible when outdoors for prolonged periods of time.