Why am I not losing weight?

I've been going to gym fairly regularly since May. I try go every second day, sometimes every third day. I didn't go at all last week but I went Saturday, yesterday and today.

I burn anything between 250-500 calories depending on whether I'm also doing weights or not, which I do once or twice a week.

But I have lost only 2kgs. TWO KILOGRAMS ONLY. My eating habits haven't changed very much but it's not like I'm eating junk every day. Sometimes not even during the whole week. I mean we had McDonalds on Saturday but that was the first takeaways we've gotten in weeks.

I haven't even dropped centimetres. I'm still squeezing into my jeans. My bum shape has changed a bit but that's it.

I've now started drinking smoothies every day (making myself, with water or yoghurt)- will that help at all?

At this stage it's like why am I bothering going to gym when it's not doing anything for me.

*I want to add that I'm not just using the same cardio machine either. I sometimes primarily use the treadmill, other times the rowing machine, sometimes I go for equal calories on numerous machines, etc.