I'm not a doctor, but it sounds to me like there is another underlying issue here, rather than you just can't move your legs around. Maybe it's your general sitting posture and some excessive muscle tension? It's pretty easy to get tense when in the early training stage. I did a vertical reference course a few years ago, at a stage where I had about 8,000 hours on multiple types, and was a TRE on 4 types. It was like being a zero hour student, and I would get back from each trip with aching muscles from being so tense! Mind you, hanging out of an open door didn't help.....
I've also flown multi-hour flights (Longest was 7:45) which just resulted in a bit of stiffness after, which stretching cured
My basic point is, that with 45 minute trips, I don't think it is natural to get sciatica.