No space of iphone, no downloads been made

I'm kinda stuck, because on my iphone 5 16gb with ios 8, all free space gone. According to usage manager i should have around 1gb. Few days ago i've deleted couple music album, and freed about 300mb, but today i see that abound 5mb left. I didn't do any downloads updates or anything else. Just phone calls. I've also checked if there was update file downloaded, but there were none. Any ideas how can i check where my space gone?