Just adding my two cents in...Where are your running? Cement and pavement can be vary hard impacting for your legs and can add to your ship splint problems. If you can I would look for some softer trails or the track at the local high school for a softer surface. Treadmills also tend to have more cushioning. Or the grass next to the road/sidewalk.
Candy, the elliptical can certainly kick your bu$$! I like it lots better than the treadmill, and get my heartrate higher too. I believe it will help with your endurance, too.