Like some of the folks here suggested if you have ANY pain that is causing you discomfort on the morning please see a doctor FIRST and follow the doctors advice....
I am a big dog and the mat thunders everytime I execute Ukemi LOL...
Technique has only so much to do with it when you're a big dog...
how's your Core Fitness? Are you strengthing it with specific exercises like crunches and leg lifts? How about Yoga? As I get older I find that if I let my Core Fitness (aka Abdominal and Hip Flexors along with mid and lower back muscles) slack... It is not too long before my Hara (aka Belly Button Center) starts to move back into my chest and I become top heavy on my rolls which results in extra stress in my shoulders and arms when I roll in am attempt to compensate for my weak core muscles...
What works for me is Yoga and Specific Core Building Exercises developed by my personal trainer...
First things first Heal Up and do some Physical Therapy if you need to...Then get thee to a gym and explain to an experianced Personal Trainer that you want to work on building your Core Muscle Groups...and
Please Lose as much weight as you can to get your BMI (Body Mass Index the ratio of fat to muscle) down which in conjunction with your Core Exercises will make you a Light Footed Break Falling Cool Dude.
Good Luck
William Hazen