Remaining positive in times of difficulty

I have alot of negativity which stems from the house I stay in. My father doesn't provide for us so I feel very depressed that I have to buy things with my own money (necessities like groceries toiletries etc.). So when my elder sister (who has more money than me) says that I should cheer up and I shouldn't be so sulky and my imaan is weak, I feel like a failure and that nobody listens to me. Obviously my Allah listens to me and there is khair behind everything but it hurts for your own family to judge you especially when you are trying to be a better Muslim and they just shatter you like that.

Is my Imaan really weak if I get sad when I have to spend money on myself? Kindly provide a dua I can recite to get this evil habit out of me.