Hi AmandaJane
Welcome from me too.
Which is which of these tablets? One of them will contain oestradiol only and the other oestradiol and dydrogesterone (the progestogen).
The idea is that HRT will make your body act a bit like a normal menstrual cycle, so most women feel better on the oestrogen only and some women (if progesterone intolerant - or at least unable to tolerate the synthetic progestogens in some HRT or in pill form) feel worse on the oestrogen and progestogen pills.
However some women are OK on both types but feel typical pms symptoms for a few days after they change from the oestrogen only to the oestrogen and progesterone ( anxiety, depression, irritability, headache etc) and this is due to progesterone withdrawal - just like before a natural period when progesterone ( as well as oestrogen ) levels drop. In most HRT oestrogen levels stay the same so only your own hormones may still fluctuate if not past menopause.
It is important to know what is happening hormone wise before you change types as the outcome will probably depend on your reaction to progesterone as above
I hope this hasn't confused you! (My fault if so!!).
Hurdity x