Hi renee
The reason your period is heavy, isn't because you didn't have one on the Climagest - if you are on cyclical HRT and you don't bleed then it means that the lining has not built up to be shed. It's not like with our natural cycle.
The fact that you have bled on this one is either because your own hormones have kicked in a bit more - and added into the mix - ie more oestrogen to build up, or because you have changed HRT. The norethisterone in Climagest is also a more powerful progestogen in keeping the lining thin, than progesterone and dydrogesterone so while you were taking the combi pills it could have helped keep the lining thin.
The other thing is the doses of the different tabs - are they both the same oestrogen dose? A higher oestrogen dose will build up more lining.
Also your fibroids may have grown slightly so more likely to bleed as time goes on.
So not necessarily straightforward but all perfectly normal!
Hurdity x