trans | Post-operative fitness in transwomen

Does anyone have any experience of getting properly fit post-operatively they'd be willing to share? I'm trying to get fit again for the first time in nearly 4 years - I'm currently almost exactly 2 years post-op. However, I'm finding it much, much harder than before and quite significantly more than could be explained by age and differeing Gender. 3 years ago I was able to run a mile and a half (2.4km) in just under 11 minutes without too much difficulty but now I'm struggling to get my time consistently under 16 minutes. (A woman my age should eaisly be able to get that time to 13 minutes or less) It this an inevitable result of transition and lack of testosterone compared to cis-gendered women or just some problem specific to myself?