You have several problems
The most pressing is you have white spot. Either get a white spot treatment or turn the temp up to 30c and leave it there for 6 days after you have seen the last spot
The second is you have far too many fish in your tank. Rehome all the fish except 2, if you dont your water quality will go bad and your fish will get ill and more than likely die
The third is your tank may not be cycled. Check this page out to find out about cycling.
www.oscarfishlover.com/how-to-cycle-a-tank
If you have any questions ask away, we are here to help