I would take off 2 and make it 5.  You really need at least 4 days per city to appreciate it.

yeah, 7 is waaay too much.  I assume you are just visiting one city per country?  In large cities you cant find your way around or even feel at ease until you’ve been there a full 2 days

Ok Lets Say : Hungary,Czech And Poland i will keep for sure.
About Germany im also not very sure, i was thinking maybe to skeep Germany too and go from Poland Sraight to Sweden, Is there a way Throe InterRail i can get maybe by boat from poland to sweden ? or i need to make the whole journey by land throe germany and denmark to get to sweden.
 
p.s how are the countries i decided to keep ? east europe i mean .. are they intersting ? night life and stuff ?

Trying to do all 7 in three weeks would just be a waste of time and money – you’d be so rushed you’ll hardly enjoy your trip. Don’t forget you are traveling some pretty far distances and have to factor in that travel time. Five countries is possible but I’d cut out another and just do Hungary, Czech, Poland, and Germany or any combination of four. You’ll really enjoy a country alot more when you can visit several cities. If you just spend 2 days each in Budapest, Prague, and Krakow and then move on – well they’re all gonna feel/seem the same. 

Poland has some ports, but I don’t think there are any major ferry services.  Even if it did, to stockholm would take at least a day or two.  Flying is probably best.  I flew wizzair from Warsaw to Stockholm/skavsta, security in warsaw was anal, but other than that everything was good. 

Also, I think you will save a lot of money if you just buy tickets instead of interRail.  Depending on how many cities you visit, the East Pass might be worthwhile; price isn’t too bad and you don’t have to deal with waiting in line for tickets, trying to talk to babuska selling tickets, etc. 

One thing to note, traveling between the the eastern countries is a lot slower and less frequent than your typical western interrail travel.  But the sights and experiences are much better IMO.  Nightlife is excellent, and a bit cheaper.
 
 

Amm thanks for the replies, i will talk with my freind and together we will choose 4 or maybe 5 countries for our trip.
Probebly we will take Sweden out even thoe i would really want to visit that country.
maybe Hungary,Czech,Poland and Germany seems fine.
maybe visiting more then one city in places like germany and poland.
 
i will see whats going on and will update when i get new information

I’ll just be the vote of positivity and say you can do 7 countries in 3 weeks. I’ve done it three times. I like to be on the go and I plan what sites I want to see ahead of time. Some how I still end up with extra time to just enjoy a park or walk around aimlessly. Night travel is a big help since you are going to be in eastern Europe where  Ryanair and Easyjet don’t fly to as much. Also I have to give a vote for Sweden since I studied abroad there and it is one of my favorite countries