Hi Lisa.
I don't know that I'd consider myself an expert ..

... just someone with a lot of experience.
I'm reluctant to say "go for it" to a weight vest, just because I don't know what kind of exercise you're doing. I would suggest that you change up your
exercise routine first before just throwing on weight and continuing to do the same thing.
I'm going to take a guess and say that it sounds to me like you're not lifting
weights as part of your workout? If you're not, you might try adding weight lifting to your routine. You also might try adding interval training to your routine.
Again, it's hard to be definitive because I don't know what you're doing right now.
Also keep in mind that it's pretty much natural progression that as you lose weight and become more in shape, that your
body won't burn as many
calories; it's harder to move 200 lbs around than it is to move 150 lbs ... that kind of thing.