Memory problems

Hi,

I have noticed that my phone memory is nearly full despite the fact that I don't have a lot of apps, photos or anything else on it. When I connect the phone to iTunes, the memory status in itunes tells me that I have 4Gb available memory, if I look at the available space on my phone (in settings) it tells me that I only have 150Mb available space left (hence the constant low memory warnings). I have been deleting photos and apps to free up space and without installing anything new or taking new photos the amount of memory steadily declines. (and how is it possible that itunes tells me I have a lot of space available but my phone tells me something else?)

So I decided to reinstall and reset my phone which freed up a lot of space. Once the update was done my phone indicated that I had 5Gb free space. But without doing much, besides reading emails, using safari and listening to Apple Music, that space has shrank to 4Gb within 12 hours. Where did that GB go? Is Apple Music blocking some of my memory?

Does anyone else deal with such kind of Memory issues? I use a iphone6 and I have the latest updates installed.

Thank you for your help.