Teenage boy has to find a place with survivors in post apocalyptic world. Pretty sure it started like that. On his journey meets a girl and they fall in love. Reminds me of the Fallout video game series kind of story. I remember this from the mid '90s. Was one of my favorite series and would love to re-read for nostalgic reasons.
This probably isn't right, but possibly Patrick Tilley's Amtrak Wars series?
- post apocalypse
- teenage boy looking for survivors
- meets and falls in love with girl
- one of the books was called "Earth Thunder"
- six books, rather than a trilogy
- the boy IS looking for survivors, but the intent is to kill them
- he's also not alone, but part of a large expedition
Possibly the Firebrats series by Barbara and Scott Siegel:
Fire Brats is a series set in the aftermath of World War 3, it follows the struggles of two teenagers Matt and Dani to escape a nuclear-bombed city and find a new life.
Matt and Dani scarcely know one another when World War 3 happens. They meet each other in a theater basement, where they live on junk food and suffer a mild form of radiation sickness.
When an earthquake destroys the building over their heads a month later, they dig their way out to find themselves threatened by a gang of escaped convicts. They escape to head for California, where Matt hopes to find the rest of his family still alive.
The description and date fit, and the third book is Thunder Mountain, which fits your description of having "Thunder" in the title.