Looks to me like you need to evaluate your eating habits more closely. I would suggest journaling exactly what you have eaten every day, and you might be surprised at what exactly may be causing your weight gain.
43 yrs old is too young for menopause, That would not cause extreme weight gain anyway in most cases. You do NOT have "live with this" and accept weight gain as part of aging. That is simply not true. You DO need to evaluate your eating habits more closely though as you age.
single word answer hormones , you are either in perimenopause or menopause , the midlife weight gain , there is lots of info on this online no easy solution either , it is the ageing thing
do not be upset you are alive and in good health learn to love yourself be friends with your body you have to live with this and accept the new you or it is the endless weight battle etc.