stretching

Hi, I am having a bit of a conundrum with a little guinea of mine and her elongating herself showing discomfort/pain. She was doing this when I first brought her home, aged 8 weeks. I thought she just liked stretching herself out - looking like she was chilling out like we all do on holidays...

When I cuddle my piggies they are usually calm and lay down and enjoy the petting. They are also very vocal and are talking to me all the time. Todays one was stretching and yawning while being cuddled. She's usually shy. So this surprised me. The other one was also being cuddled after that and...