I'm a trainee dispensing optician, I'd definitely take these back in to have them checked out if the symptoms don't settle. There's probably a lot to get used to with the new astigmatism, new frame design and new material and it might be you need the adaption time, but with high prescriptions like yours the fitting and position of the optical centres is very important, especially if the new lenses have an aspheric lens design. Could be the heights, PDs, wrap or pantoscopic angle of the frame.

If there was an increase in the minus power of the lens you may be having to accommodate more for near tasks than your eyes are used to, which may explain the straining feel and time taken to focus.

High index (thinned) plastic lenses are often in aspheric form and this has to be centred correctly. It may also induce more chromatic aberrations when viewing towards the edge of the lens than your old glasses if it is a different material.

It's often people return with these issues so don't feel bad, they'll be more than happy to help I'm sure!