Just checking to see we have covered the basics. Do you backwash and rinse your sand filter twice before returning to filter mode? Full instructions are in the below link
http://www.troublefreepool.com/content/144-maintenance-and-cleaning-of-pool-filters
Do you backwash when your filter pressure goes up by 25%? They work better a little dirty, but not a lot dirty
Does your gauge go to 0 when you turn your filter off? If not you need a new gauge, very easy to install and only about $8
It sounds to me like you do need to deep clean your filter. I would watch the videos a couple of times, ask questions if you are unsure and when you feel comfortable about it give it a go. It really isnt hard to do but understand you may feel daunted or overwhelmed with everything right now. If you take it slow and carefully you wont break anything, when you feel ready. I know the first time I did mine I felt like supergirl and that I could conquer mountains, lol :super:
Sand filter cleaning video links direct from Youtube
https://www.youtube.com/watch?v=MpNEBIIR5P4
https://www.youtube.com/watch?v=1wBhwYv_RKI
Oh BTW you never need to replace sand except in rare circumstances, it was already a couple of million years old before it got to the filter, a couple more years wont hurt it

I even studied geology but it took someone on here to point that little fact out to me

For now enjoy your pool, I mean that's whats its there for. I tell myself I have to '
observe' my pool daily, for its health, while sitting in the sun watching the sparkles off the water. Sometimes '
observing' can go on for hours and I have to consume adult beverages just so I can cope with all the
stress of floating round the pool in the sun:splash: