Have you considered something like a Sorbathane heel wedge? If your other shoes have a higher heel to mid-foot drop, they would ease the added strectching on the achilles and provide additional cushioning that might be lacking in the spikes. Best to put them under any insole, to stop them slipping forwards, or tape them in place.
Probably more of a loading thing; no running in spikes for ages and then a fair amount of use over a few weeks. It's feeling fine now after a bit of a rest.