Izzy took 10 months for her ears to stand straight properly. Apparently, the more things they can chew on the better, Chewing strengthens the muscles in the cheek and the base of the ears. The chewy 'marrow or hide' sticks you can get from pet shops are great. Another reason they might not be standing is infection or allergy.
Izzy has a really sensitive stomach and if she eats the wrong thing, it shows in her ears, they flop until I give them a good clean. If it's a smelly brown colour, it tends to be a build up of yeast that then causes an infection, or they might just want a deep clean, in which case massaging his/her ears at the base will loosen it all up. Don't go sticking your fingers right down the ears though, better to see a vet and get some drops
Good luck