Oh, dear. Every time I see an eldest daughter talk about personal pressure, I do my best to validate their feelings because I understand how tough it is. The reason you don’t know why you feel such pressure despite not having any from your parents is because society shaped your perspectives on the responsibilities of the first child. Plus, you really care about your family and making a good life for yourself, so the pressure is expected.
I’m glad that you end up relaxing and letting things be when they’re not going your way. Life will get better. Hugs!