I am trying hard to earn so I can marry soon and support my father, but I am unable to earn enough. My father is getting weaker day by day, and I feel guilty that I cannot help him. The pressure keeps increasing. What should I do?

You are not sinful for what you are unable to do, because the duty of spending on a parent is tied to capacity, and Allah Jalla wa Ala says, the meaning of which is: Allah does not burden a soul beyond its capacity (al-Baqarah 286), so put the guilt down. Keep taking every lawful means while insisting in dua to Allah, and hold to taqwa and istighfar, for He says, the meaning of which is: whoever fears Allah, He makes a way out for him and provides for him from where he does not expect (al-Talaq 2 and 3). Keep in mind this is a general answer for your question as you did not provide me with more details.