I've got one in a pot and several planted out in the garden. They like the sun and do well in our garden which doesn't have the ideal soil, being clay, but once established they have thrived. The one we have in a pot is not in full sun and we try to ensure the soil is kept moist but not waterlogged. If I were you I'd probably repot it to check there's nothing eating the roots and then put it where it gets some sun but not full sun. Good luck it's so annoying to lose plants but generally they are quite easy once they've got going!