Girls, I just made a cup of RLT from loose leaf tea - and something is wrong! Maybe!

I had one yesterday that was fine, it didn't really taste like anything, so today I made it a bit stronger (two tsp instead of one) but that's all I did different.

I left it to steep for the appropriate time (5mins) but when I took a sip, it was terrible - ok at first but then a really bitter aftertaste hit me. I've added two sugars so its nice and sweet but the bitter aftertaste persists!

Did I make it too strong? Should I be taking more weak cups, as opposed to fewer stronger cups?

So confused.