People tell me to be patient as a second wife, but I feel pressured from bottling everything up. What should I do?

Patience does not mean holding things in until you fall ill; it means facing a trial without doing what is haram, while still expressing yourself in the right way. The Prophet Ya'qub was patient, yet still said: “Indeed, I only complain of my distress and my sorrow to Allah” (Surah Yusuf 12:86). So pour it out to Allah in prayer, and to your husband or someone you trust in a good way. Prolonged bottling up can turn into stress and illness; that is not the patience that is required. State your needs and feelings calmly, not in an outburst. If the burden is too heavy, get help from a counsellor. Healthy patience strengthens you rather than destroying you. See mental health.