u/Tarigrade

First image is my back, (censored for privacy). Second image is a close up of the markings.

They suddenly apeared overnight about a year ago, they are not from any weight gain, and their being horizontal makes it unlikly that they were from height gain either. They are very noticable in real life because they are a deepr purple in person.

I got my yearly physical yesterday and my pediatrician told me she dont think its a skin condition and she can only assume they are stretch marks but she is very confused because they should be vertical. They arent scratches or scars either. They havent faded at all over time and im just baffled as to what they could be.

If anyone could even just guess it would really be appreciated!