Im trying to download apps but it says insufficient storage but I have plenty of storage and an sd card
I had the same problem on my Huawei Ascend P2, I did a factory reset and it seemed to work, though I highly recommend copying over to your computer every file on your phone before even trying to do so, I don't know the cause myself, the theories I have are:

Virus
Damaged internal memory

If it still doesn't work after the factory reset then you need to take it to a specialist (unless you are one) and take it apart and replace the memory. 

P.S Don't treat this as a answer as such, I don't have the reputation to comment (which I think they should allow everyone to do instead of risking losing a ton of rep).

P.S.S Have you checked to see if your SD card is being read by your phone?