I feel a burning sensation under my armpit. I suppose it's because the cup is putting pressure on it, but I'm afraid I might be damaging a nerve. I don't know if it's just paranoia, but I've noticed a very subtle tingling sensation in my shoulder (I'm very hypochondriac). And no matter how low or centered I place the cups, they always end up positioning themselves in a way that causes pain in my armpit. What do you think?
Stop pumping until the pain goes away, this can be serious. In order to move the cups away, try pumping with one cup only (alternate sides every 15 minutes), this way you can more easily center and move down. If it rides up, try something like wrapping a towel around above to keep it down. Also try padding.
If repositioning away from your armpit doesn't work, you may need to use a smaller dome or, as suggested above, only pump one side at a time if there is no room.
Does the dome you use have cushioning? If not, that might help as well.
Had a similar sensation briefly with evebra but repositioning the domes closer to the center and at an angle stopped it and I've never had an issue with it since.