Riding bicycle without using seat I've almost always rode on a BMX, so I've never been sitting while riding because of how low the seat is.Now I've had a chance to try out a more normal bike but I found sitting on the seat to be very uncomfortable so I've been riding several km standing.

I've also tried many different seats but they were all too uncomfortable. 

I'm quite concerned that if I start doing this everyday Ill develop some leg problems (like blood circulation maybe?) or have other issues.
Traveling long distances on a bike seat is almost always going to be uncomfortable when your body isn't used to it. Give it time.

But also, consider taking your bike with you to have a professional make sure the seat and the bike fit you. Some people have managed to permanently damage their blood vessels ( I won't go into detail ) by improperly sitting on a bike seat. Call around to see if there's a bike shop near you that can help and ask how much they'll charge you.