How tall are you ? Perhaps the reason your weight loss is slowing is because you're close to a healthy weight for your height. The closer a person is to a healthy weight for their height, the harder it gets to lose any excess. So, depending on your height and how much more weight you need to lose, you may just need to be more patient.
You've already lost quite a bit of weight and you've kept it off. That's fantastic ! Why aren't you losing more ? Once again, hard to say because we don't know anything about you or what you've been eating over the last few years. it could be because you're nearing a healthy weight for your height. If you're down to that last 5-10 pounds, this will be slow going. Someone who is morbidly obese could lose 1-2 pounds per week. However, once again, if you're nearing a healthy weight for your height, losing the excess will take longer.
Do you do any type of strength training ? Walking is great, keep walking. But if you want to change your body, you need to strength train. Add lean muscle because muscle burns fat. the more lean muscle you carry, the more efficient your body will be at burning fat. Also, a good strength training program can help you to lose inches without losing any scale weight. it's a matter of changing your lean to body fat ratio.
Because you're a guy and have a higher percentage of testosterone than women, your body will benefit from a good strength training program quickly. You may find that strength training will do more for your body than trying to lose that last five or so pounds.