HI OP, I just want to chime in with PPs who note an element of control here which you pushed against.
You said that his response may have been “no I don’t want you to do it, I think it’s a stupid lazy thing to do".
Whilst accepting this was a description of a typical response and not a quote, it appears that you ARE affected, in decision-making, by his views, prejudices and importantly, his approval.
I would think about that. Is his disapproval painful for you and so you avoid it? Is this a time you were trying to be autonomous?
As a couple in a respectful supportive marriage this should all be considered in the round. Discussion about what led you to want to conceal this. That this weight issue was important enough for you to want to have sole control of it and not (for once?) accede to his views. How to be open, non judgemental and support each other better.
I've never had a relationship which works like this, as it should - so I'm not preaching - I know exactly, viscerally, why you concealed this and it's not because you're a liar.
Many people in his shoes would be mortified that their loved one felt compelled to hide this.
The issue of your weight/BMI/the meds is separate really. I guess if you were prescribed it then you required some weight loss for health. And it's tough, using that medication to gain health, it's not an easy option.
Ah I hope you feel better today (or maybe tomorrow when you've had a sleep). You've apologised. Tell him that's all you can do, that this is the one thing you've ever concealed. And that you're aware that his disapproval and criticism were what you were keen to avoid. Say that's something you'll be working on in yourself. Cos no one is perfect.
Please don't apologise forever more. If he holds it over you long term that's twattery and not husbandly/loving behaviour.
You have not fucked anything up.