Help please - weight gain

Im looking for some advice, help, tips.
2 years ago i lost 42lbs, over christmas i put on 3-5lbs but once i went back to my exercise and food regime i lost the weight and was able to maintain until this year.
At christmas i put on the usual weight but when i returned to my regime nothing happened, and then over the last 2 months my weight has begun to go up.
I walk 5.8km in 50 mins 5-6 days a week. I eat 1500 or less calories a day and my weight is going up.
I am now completely demotivated and frustrated and looking for anyone with any ideas why this is happening

I am sorry to hear you’re demotivated and frustrated. That is never easy. Can you be more specific on your diet? I follow and easy three step method:
1) Dirt (what I call crazy amounts of veggies, in all varieties, the most recognizable ingredient in every meal).
2) Fat (olive oil or nuts for me, I try to go light on animal fats)
3) Protein (fish, poultry or meat, only 2 oz. cooked per meal).

I try to never eat anything with a label, no sugars (that applies to corn sweetners, honey, molassis, etc.), no grains.