Sound too low when using headphones

Today I noticed when I use headphones the sounds is very very low to the point I can barely hear anything. This happens with almost all applications, except when I use the phone app. I can hear much better but still low. Phone charges fine so I suppose the jack works to a degree.

Below you can see the things I have tried:

1. Shutdown / Start up the phone
2. Clean the headphone jack
3. Upgrade to the latest OS
4. Try a different headphone set (same thing)
5. Try headphone set on a different phone (it worked just fine)

specs: iPhone 7, iOS 12.1.4

Does anybody know what could be wrong?

Thanks