This summer, I took a river cruise with my dad in Melbourne. This summer, I took a river cruise with my dad in Melbourne.

I made a really big mistake: I forgot to bring my sun hat, and I didn't put on sunscreen because it had been cloudy the pastrevious few days. I made a really big mistake: I forgot to bring my sun hat, and I didn't put on sunscreen because it had been cloudy the previous few days.

“The past few days” refers to the few days prior to today. For a few days prior to a point in the past, I would say “the previous few days.”

I made athe really big mistake: I of forgotetting to bring my sun hat, andAND I didn't put on sunscreen because it had been cloudy the past few days. I made the really big mistake of forgetting to bring my sun hat, AND I didn't put on sunscreen because it had been cloudy the past few days.

The "and" does not need to be capitalized here, I just did that for emphasis.

I put on aloe vera gel every day for the next few days, andFor next few days after, I wore aloe vera gel, and even then it still took about four or five days to recover. For next few days after, I wore aloe vera gel, and even then it still took about four or five days to recover.