This is right. You're going to need smaller plates as you will struggle to keep adding 2.5kg each time, deadlift should be able to do 2.5kg each time though.
If you can't get the 3x5 for a particular lift for 3 consecutive workouts you need to reset the weight (from memory 10%) then work your way back up. As a general guide, people say if you stall and reset on the squat 3 times, it's time to move on but too me that is a big generalisation.
If you are stalling then it's a good idea to check diet and if you're getting enough sleep. You should also keep a pretty basic log of lifts etc.