Breaststroke help

I am new to masters swimming, and had not trained since 1988 until a couple of months ago. I am not exactly killing it yet, but I am finally getting a feel for the water, and I cranked out a 1200 workout today and it felt like I was just getting started. Anyway, to the point ... I was a breaststroker in the old days, and I never learned to swim with my head going under in my glide. About a month ago, I decided to try it (with help from some old posts here). I finally got the rhythm down last week, taking my strokes per 25 down from 12 to 8/9, but it feels like I am putting way too much strain on my inner thighs during my kick, resulting in some mild groin strains (both sides)from trying to go to fast (kicking too hard, if there is such a thing). Is this just a matter of getting used to a new angle? I can breaststroke kick only for as long as I want without trouble, but as soon as I put in the big glide, ouch. I swam plenty of breaststroke today without pain, but I went easy on the kick. I appreciate any advice. -Jim L