Everyone is different, and being on the optimum dose for you is the most important thing.
If you feel MJ isn't being as effective then it's definitely time to move up. (ie hungrier in-between meals/urges to eat/cravings etc).
It is a smaller jump, dose-wise, between 5 & 7.5mg compared to when you went from zero to 2.5, and then 2.5 to 5mg.
So you should notice the difference but it won't be as bigger jump as before.
I found moving up very helpful.
After a month, If you find 7.5 has little effect, then move up to 10.
Also, just to double check, are you eating mainly protein and vegetables, drinking LOADS of water and doing some exercise?
I stay well away from white carbs, and only have a small amount of 'healthy' carbs occasionally. I know this doesn't suit everyone, but I have found that as I got a bit older (late 40's, now mid 50's) carbs effect my digestive system differently and I just can't lose weight if I eat them.
I don't count calories and am losing well, however a lot of people work out how many calories they should be on in order to lose weight. Sadly, your calories to lose weight will drop as you get slimmer.