You have to file a US return if your worldwide income meets the filing threshold- it doesn't matter how much was earned in the US. US citizens report their income from anywhere.
The threshold is $10,350 in US dollars (equivalent).
Click begin at the bottom here:
https://www.irs.gov/uac/do-i-need-to-file-a-tax-return
Also, keep in mind that overseas taxpayers have extra time to file, and the deadline is never particularly relevant if you don't owe taxes.
You probably do need to file. However, you probably don't owe tax or need to worry about getting it done today.
