OK, so, he's stopped the nightfeed because the formula fills him up and it takes him all night to digest it, so the sleeping for 6 hours+ and the return of your period are almost certainly connected to the 11pm formula feed. I think if you start to offer him more feeds in the day and resist the temptation to give more bottles then you will probably be ok.
Don't let the HV pressure you to up the bottles, as long as he's not losing weight then if he drops down some centiles it doesn't matter. Both mine have fallen down the centiles, DD1 went from 25th to 0.4th in her first year, but, she didn't lose weight, so it wasn't a problem. At the end of the day if he's happy, sleeping well, alert when he is awake, weeing a pooping plenty,looking healthy and not losing weight, then there is no need to do anything. And, he is your baby, your HV can't make you do anthing, she can only make suggestions, and it's up to you what to do, you don't have to do what she says.
The BfN has lots of info onbf compatable anti-d's, if you are struggling with anxiety and insomnia any way then perhaps it might be an idea to look into treating them earlier rather than later?
I do know that my supply drops a bit when I get my period, but it comes back again after a day or two, so don't worry if he's a bit fussy when he feeds, just feed him on demand, swapping from one side to the other and back again, and your supply will pick up again.