The detergent goes in the left-hand side compartment in our washer (and did in the machine in our old flat as well). The right-hand side compartment on ours is for fabric softener. Have never used the small, middle one, but assumed it was for bleach. Do you have access to the manual to find out where the detergent should go? Sometimes you can find manuals online, if not.
ETA: Also, if you are in an area with very hard water, you probably will need to use more detergent than you normally would. There is usually a hard-water suggestion on the back of detergent. Using a water softner every so often will also help to make sure that the soap works better.