Hi Sam,
Be careful with the 'trapped nerve' diagnosis as it is a weak one. There are two thing that cause a 'trapped nerve pain' and neither of them are muscular
1. You had facet joint or capsule irritation.
2. You had a disc lesion that put pressure on you nerve roots. Sciatica, common in 20's
Both can cause pain from that dimple at your lower back and radiate into buttock but often feel different.
1. Feels sharp when moving and often revert back to a stiff achy pain when still.
2. Feels like you hit your funny bone with a tingling sensation going down the back of buttock and possible even further.
The likely reason this started was bad posture leading to weakness in the very small intersegmental muscles of the back.
much like a sore foot, if a vertebra has a pain your body will start to use another vertebra, similar to a limp. The pain often feels like its gone but actually is merely be guarded by you restraining movement.
This will put more pressure on other vertebra - This can lead to another worse pain developing.
As another consequence: A habit can form of not moving from the injured vertebra segment - This means the disc which also could be a source of pain will not get as much movement and wont suck as much nutrition from vertebra marrow. this leads to disc degeneration
long and short you have had a minor episode but you should get a few sessions of professional advice to identify poor movement patterns post injury, identify the weaknesses that caused complaint and get some ergonomic advice about sleeping/work postures.
The investment now will safe guard you for future occurrence.
Hope that helps,
Niall Marshall-Manifold
Wimbledon Chiropractic & Sports Injury Clinic