Hi. It’s very difficult to say without seeing you play. I’m 42 and I’ve picked up the guitar again in the last 18 months. I dabbled in in my 20’s but only for two years and now starting again more seriously I realise how many bad habits I had from not learning properly initially.

In relation to your question the biggest technique I’ve had to relearn is to fret the guitar as much as possible with a straight wrist rather than having your hand bend up 90 degrees towards the low E string. Also, it could be that you’re unconsciously supporting the neck of the guitar with your left hand while playing.

As I say, it’s really hard to say what’s wrong without seeing you play but just do a YouTube search for something like ‘correct guitar posture / correct fretting technique’. There’s a wealth of info on there. Just be wary of taking YouTube advice from reputable sources.