I've been in an endless cycle of losing and gaining the same 4lb for months now

it's driving me up the wall now! My original target was 9st, I got there and decided I wasn't happy and wanted another 1/2 stone off. Since then though I've fluctuated between 9st and 9st4, occasionally going a bit higher if I've had a massive blowout!
I was talking to a friend the other day and she said she didn't think I needed to lose more and she's convinced everyone has a weight that's right for them that they'll settle at! And she thinks the reason I can't shift any more is that I've hit my natural weight.
Thinking logically and rationally, she's probably right! I'm eating comfortably ATM, eating what I want, which includes the odd chocolatey snack and a beer and takeaway night on a Friday. So I either focus really hard and try And lose 7lb-ish that I may never lose, or relax a bit and just try and enjoy myself!
I know my main thing ATM is that I need to tone up, although exercising is proving rather tricky ATM with everything else that's going on!
Thoughts anyone? I'm between an 8 and 10, on a 9st day my 8s are comfortable, on a 9st4 day I may pull out my 10s. Ive been dieting that long now though, I don't know what it's like not to be watching what I eat!