Problems downloading any apps on my Galaxy S5

A

AC Question

Well, the proplem is simple. When I go into Google Play Store to select and download an app, it either says it's 'installed' (of which it ISN'T!) or 'this app will be available shortly' (of which it never IS!). Been into my list of apps under 'settings' and that only shows what I already have on my desktop. There's no mention at all of the apps i've since tried to download for MONTHS, and they were the ones that i got the message "this app will be available shortly". I've checked the 'allow apps from unknown sources' bit, and that's fine, even though I only download from Google Play Store anyway. Will SOMEONE please tell me what's going on here? I don't want to get drastic and 'factory reset' my fone, as i'll lose all my personal stuff (haven't any way to back them up - my fone IS my computer!) so what will I do? And another thing: when I do go through the 'install' bit of that app, there's logos of a mobile fone and a tablet ....... obviously I suppose you're supposed to click-on the fone one of you want the app to go on your fone, and click-on the tablet if tlyou want the app to go onto a tablet, yes? BUT, it's never coming up with my model of fone OR tablet ....... could this be the problem all along? The app in question isn't AVAILABLE for my fone model? HELP!!!!!!!!!!!!!!!!!!!!