you need to work on your core dailly as well as your arms and shoulders. It is your core that supports everything else and takes the stress off your shoulders and arms as well as supporting and providing leverage and strength for your legs. Work into the riding slowly, go slightly over your absolute comfort level but not to the extent of injuring yourself. Personally it takes me at least 200 miles to adjust and toughen up to a new saddle even if it is exactly the same make and model as the previous one and somewhat less time if I tweek my fit in any other way.

Hang in there, strengthen up your core and arms and shoulders and work into the miles and if it doesn't get better, consider a refit.

go you

marni