“When I walked here from my house, my belly shrank.”
“When I walked here from my house, I got hungry.” (Thanks @Belthazar!)
It could probably be phrased a little different because of the んだ and もの, but I’m not really confident in exactly how. Maybe start with “The thing is…”?
I actually had a question early in the thread about きたら/歩いてきたら myself, so I can answer this one :).
きたら is the たら conditional form of くる (plain past form + ら.) And くる attached to the て form of a verb can mean the action took place toward the speaker/their current location–that’s why I translated it as “walked here.” The conditional part is the “when” at the start–it could be “when” or “if” (or possibly other things?), but “when” seems more appropriate here.