Yes, this is definitely not surprising. Here what's probably going on. When your glucose levels are low, you become hungry. One way to increase the glucose levels is to eat food. Adderall increases your glucose levels artificially by stimulating the production of epinephrine (adrenaline) in your which then mobilizes your stored glucose. In the short term, you lose weight. Nevertheless, you have just artificially increased your glucose levels, so your body only thinks it is full. Overtime a couple of things begin to happen. 1) Your cells adapt to the effects of the stimulate, hence, your body does not mobilize as much glucose. 2) Also, your body begins to depend on the Adderall to keep the glucose levels stable. In other words, overtime when you take Adderall, your glucose levels are now what was normal a while back when you first start. Additionally, your glucose levels drop below normal when you are not taking the Adderall. Therefore, unless you continue to increase the does (which at a point becomes dangerous), you actually begin to become hungrier when it wears off then you were before you started.
Another problem that does not help, is the fact that Adderall suppresses your appetite which in turn causes you not to eat. The stimulate effect itself does very little to boost your actual metabolism. In fact, when you cut back on your calories, your body has a tendency to burn off muscle. Muscle is very active tissue and the more muscle you have, the faster your metabolism, so in essence, Adderall in this way can actually slow your metabolism. Therefore, unless you are doing resistance training to offset any muscle loss due to a calorie deficit, you will find that overtime, you will need to consume less and less calories to maintain your ideal weight.
In fact, over a 5-10 year period, Adderall and other amphetamines are not very effective at weight loss. This is why doctors are hesitant to use them. Also, they have a higher potential for abuse than other drugs, however, when use correctly, they can be very effective in aiding in concentration.
One thing you may want to consider is trying a version of the drug that is time released like Adderall XR. While this may not solve your problems, it may help manage your problems a little easier, since a time released version gradually wears off, thus making it less likely that you will have a glucose crash after the drug wears off.