Groin pains? what is this?

I'm about 20 weeks along now with my second pregnancy and it's been more or less uneventful and normal, but for the past week I keep getting these really strange pains in my groin area.  It usually happens when I step over something (i.e. DS's trucks, baby gate, anything more than 1 ft above the floor) and it doesn't happen WHEN I'm stepping but once I continue walking, and then I have to take these tiny little waddling steps for a couple minutes til it feels better.  It's this really awkward tightness that sends shooting pains down my thighs if I try to walk normal when it happens.  Anyone have this happen? Anything I should worry about?  I'm going to tell my Dr about it at my next appt (unless someone advises I do so sooner).  Will this require pelvidc rest or something?  Any info or advice would be great! Thanks!

P.S. this problem doesn't happen during sex or even if I dance around the house or exercise, only when I am stepping over something that involves forward motion. (like "lunges" kinda)