What Causes Swelling And Bruising At The 5th Metatarsal Base?

i have swelling and bruising on the top and bottom of my foot at the 5th metatarsal base. There is also a dark line of bruising on top of my foot. I can walk on it but it is uncomfortable. I broke this same bone on my other foot a few years ago and this is less painful so it may not be broken....do i really need to see a doctor or will this heal on its own? No specific cause for this injury though I did run 5km the day before with no injury or pain??