Hi there,
Most patients get aches and pains at the start. It's all a big shock to the body, and the mind. Muscle pain is a pretty common one, and for most people it does go away or at least reduce a lot. The 90 day timescale your doctor gave you sounds reasonable but you might find things go a little faster, or a little slower.
However, if things don't get better you may have options. I had severe leg pain with imatinib - walking much over 100m was a challenge. So, we gave it time and when it wasn't getting better we switched me to dasatinib and things improved almost immediately and very soon I had no more leg pain. So don't fret - either things will improve on their own, or you have different treatment options (assuming other TKIs are available in your country).
In terms of things you can do now to help relieve the pain, it depends on the kind of pain. I'm guessing a fairly dull ache? That's quite common. Some people find magnesium cream or magnesium oil helpful. For cramps, it's important to stay well hydrated and a bit extra potassium in your diet can help - bananas are a good source. Massage may feel good and provide temporary relief too. Heat pads may feel nice.
If you use the search feature on the top right of this web site, and type in "leg pain" you'll see that you are not alone and many others have suffered from this in the past, and you will find some other ideas how to cope with it until it hopefully goes away by itself.
David.