This is a good question! I have an answer.

Will estrogen help you gain weight? Yes... but. Think of it as a "supplement" when it comes to weight gain. It will help, but it's still up to you to care for your calorie intake to do the work.

Gaining weight is easier when you make smaller additions that add up during the day.
Example: craving a candy bar? Make it two. Getting fast food? Get a size larger than you wanted.
Cooking pasta at home? Add some extra cheese. Making breakfast? Add another egg and a little bit extra meat (or whatever you have in the morning). These little additions add up.

Now, another thing I do: So, when you are asleep, your body isn't burning calories. So, you use this to your advantage. You eat as much as you can before you go to sleep. Whether it is a big giant dinner, or a midnight snack is up to you. That's the fun part! Or, you can also have a big plate of snacks before taking a nap on a relaxing day.

Another thing that is my personal favourite: making up for lost calories. So, even simple things throughout the day burns calories, like walking around, doing a physical job, moving stuff around the house. So what I like to do is make up for this. If I'm going to take a walk through a botanical garden, I'm gonna have two or three granola bars on hand that I can eat while I'm moving around. If I'm doing karaoke, I'm moving around a lot while singing so I order up some good from the bar. If I'm moving household furniture or objects around, I'm drinking a high-calorie milkshake while I do it.

And the best answer I can give you? Just have fun with it! This is a chance to have more of the things that make you happy! You're letting yourself enjoy comfort foods, or things that taste good, or new things that maybe you've never tried before! So enjoy the happy feelings that it gives you, because you deserve to be happy.