Help where am I going wrong

I would drop carb limit to 100 or 50 grams if you can handle it. Maybe drop calorie goal to 1200 max. Lower the amount of exercise calories you eat back, increase cardio by 100 calories burned per day, stop cheat meals/days. Think about using a laxative, clean out your system before weigh in day. Water should be 1/2 your weight in ounces. Retention could be contributing. Inflammation could be adding to your weight. Taking anti-inflammatories? Sorry I can go on and on with your question...

Wouldn't say it was a drastic change come jan. Id given birth in nov 12 so had spent 2013 getting back down to pregnancy weight which I hit 10st 13 in oct time then I sort of slacked off and over nov dec had gone back upto 11st 12 mainly from eating take aways 3 kids 4 and under so was grabbing food on the go plus Christmas new year ect. So come jan stopped to take aways still have the odd treat but nothing like I was and started up the exercise again. I'm using the Polar T4 don't always eat my calories back. Well very rarely I do as I find I gain.

I trust the logging of cals side I scan bar codes weigh items on scale or measuring jug for liquids and double check with packaging.

Ditto to not trusting scanning anymore.

Vendors keep the SKU and change the size all the time, which changes the calories and macros. Usually down per serving.
So could easily be eating less than you think depending if items have gone down.

But servings per package is almost never right, when you actually go by weight.
So confirm you divide the package weight by the weight per serving - if you eat the whole package or part of it. Or weighing out your portion of course takes care of that.

So with kids running around during the day, I hope you honestly selected Lightly Active as your MFP activity level, you can't be sedentary.

So why use the HRM if not eating back exercise calories?

You've likely given yourself such a big deficit, your body has adapted and lowered your daily burn.
You no longer have a deficit in place - if you trust your logging.

So - you have 2 options, guess which way will get ugly.

Cut 250 calories out of current eating level, and see if you indeed lose 1 lb in 2 weeks, and keep losing at that rate. Hope it doesn't slow down even more and stop again. Direction then will really suck.

or

Assume you've likely been eating too little for level of activity and body has adjusted, and give it a break for a few weeks, be eating closer to estimated maintenance. That means exercise calories too.

Oh, always keep the math in mind.
How long after eating back exercise calories did you gain weight? Like, how much in what time period.
Realizing that if it was fat you really gain to even be concerned about, you'd have to eat OVER your true maintenance by 500 calories daily to gain 1 lb in 1 week.

So if you ate back your exercise calories of 300 for 2 days out of a week and gained 1 lb in those 2 days - you realize that is water weight, right?

Don't be too beholden by the scale. Get out your calculator and assure yourself.