Thanks for encouragement and ideas! I think a bike fit will be my next step, part from keeping cycling and also doing stretches and some exercises.
I really look forward to next summers´ sportive - it will be a real achievement if I can make it around that lake (together with about 30 000 others!!! They release 50 riders every 2 minutes all evening and all night!), all those 300 km (186 miles), my goal is under 15 hours and I will start at sunset and cycle all night. If I can do that, I will be totally pleased with myself at 55! (I promise I´ll let you know how it goes!!)