What helped me to learn about portion control years ago was Weight Watchers. Have you tried them or a similar group?
Do you keep a food diary, so that you really know what you eat every day? It's easy to "forget" a few bites of this and that, without realizing that we are consuming more food than we realize.
Do you taste foods for seasoning while you're cooking in the kitchen? There is a big difference between putting a drop (!!!) of food on the tongue vs slurping a whole spoonful (several times) to see if the saltiness is correct. My suggestion is to stop using much salt at all while you're cooking, and put the salt shaker on the table. That way, you don't have to "correct the seasoning" as they say in the cookbooks, and consume lots more (spoonfuls of) calories before you even sit down to eat.
Are your clothes fitting looser, even though the scale says that you haven't lost? Sometimes we are doing everything right, and the scale insists that we're not. But if we are losing fat at the same time we are gaining denser muscle from doing more exercise (good for you!!!), then they sort of cancel each other out in the beginning weight-wise. But our bodies really are getting healthier, and it'll show up on the scale later.
A recent book that I found interesting is "Mindless Eating -- Why We Eat More than We Think" by Brian Wansink, Ph.D. The title says it all -- we humans can sure fool ourselves!
I wish you the best. It's frustrating. But hang in there!