side cramps when walking

I'm 18 years old and in decent shape. Since coming to college, I've walked a lot more than I usually do. Over the past two days though, every time I start walking I get what feels like a side stitch on my left-upper abdomen. Ten or fifteen steps into walking, it starts to hurt just like a side stitch
would. I was wondering if it's just a side stitch resulting from a
sudden change in my walking habits AND if it's even possible for side
stitches to last that long, or if I should be concered that it's
something more serious like a swollen spleen or anything else.[/quote]