HUGE difference in metabolism from 20 to 30 years old?

ziggyvic

When i was 18 I looked like a boy, hated my body so purposefully gained 40lbs over a short space of time- stuffing my face with junk. Clearly, the results were a bit of a shock- I went on a diet again after a year or so and lost all the weight without a great deal of effort. Just by cutting carbs really.

At the grand old age of 29, I am back up to 140lbs, which for my slight frame and height (5,5) is just too much. I have been working out like crazy for about 6 weeks, eating low carb high protein and have lost NOTHING. I don't look more toned, I don't feel slimmer.....I am tearing my hair out. Is this just a product of age? What on earth do I have to do different? I run 5k, cycle 20k (at least) and lift (ok, not heavy but i am trying) 5 days a week.....do I need to lift more and cardio less?

Please anyone been in this situation and found the answer? What am i doing wrong?