Hi Heydar,
Welcome to this message board! In agreeance with Toothless, there is problems about who you are, and where you are from, we are all here because we care for goldfish!
Toothless's advice is all good, there is not much more I can add, I'm in total agreeance with what he has to say, yes, your tank is too crowded, it will be a struggle to the end with the amount of fish you have in your tank, I know you can't give your fish away, can you get another tank? Or even another container like a bucket to keep them in? you have an aerator, you could get multi adaptors for the aerator tube and have have air going to more than one container.
Also, you will need to change the water on a very regular basis, 50% twice a week, to keep all the fish waste down (ammonia and nitrItes).
Your tank will definitely benefit from having some sponge filter attached to the end of the aerator stone, again, toothless's link to the filter page is a great place to start.
And yeah, best not to treat with PP again unless the fish really does have parasites, PP is a really harsh treatment and it wont 'cure' your fish unless your tank conditions are perfect (ie water has no ammonia/nitrIte/ low nitrAtes), you will do more damage than good for your fish.
I'm sorry to hear of your dilemma, it's unfortunate that the person who sold you all these fish for your tank was not more helpful in letting you know how to look after them. Don't give up hope yet, this messageboard is a wealth of knowledge for fish hobbyist newbies, you'll learn how to care for your fish very fast!
Good luck, and remember, we are all here because we love our fish, it is difficult to know the facilities that are available in Iraq for you, so I apologise in advance if I have made wrong assumptions about your situation.