HI!

How are you guys?
Feel free to answer that question before answering the next one

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Anyway, I have been working out almost everyday for the last few months! I have been doing pretty well too, in my opinion. At first it was a struggle, and still can be a struggle, but I am improving and it's all I ask for....
In December of 2015 I was 135 lbs. It is very difficult for me to gain weight and I have a very thin frame. However, as of two days ago I am 150 lbs!!! Woo woo!
Everyone keeps telling me that they notice that I am getting bigger, but I don't really notice at all.. but whatever!
The question: What workouts do you do for abs at the gym? To be honest, I NEVER workout my stomach. It's the one thing I don't work out.
I workout my back on day 1, shoulders on day 2, legs on day 3, arms on day 4, and chest on day 5. I dont have any ab workouts integrated at all. The more I eat the more flabby my stomach is starting to get too. So, I want to make sure I start to workout my abs before I start to gain weight.
I might sound stupid, but bare with me. I am still learning!!!
So, can anyone help me

????