Any suggestions for a discouraged 40's something mom to lose 15 lbs?

I gained 10/15 lbs last Nov. and can't shake it. Is this the dreaded middle age spread? Is this the same thing as pre-menopause weight gain? If not, what's the difference and will it go away? How long will it take to lose if I do weights 3 x's per wk and ride stationary bike 3 x's per week, both 30 minutes each?