I too would wonder if something had happened to affect the sense of taste, but assuming that it is just the tea, then I would agree with using loose leaf. My own choice is Co-op, 1 bag (250g) 99 mixed with 1 bag (25g) Indian Prince.
A few years ago, I had a nasty cold, and believed I had recovered, I was certainly tasting most things OK. Not having had a glass of wine for a week or so, I poured one and said to DH 'this is corked'. He didn't think so, so I said 'well it's horrible' and he said 'you chose it because you like it'. So I realised that there was some lingering problem. Sure enough, a few days later, I had another glass and it was lovely!