Many doctors take bribes (not actual bribes, but free gifts, First Class flights, etc) from differnt pharmacutical companies. This is supposed to persuade them to prescribe the drugs from these companies (ever noticed why so many doctors have calenders, pens, and stuff, all with names of drugs or drug companies on them?). Not all doctors pay any attention to this, but some do. So if you go to your doctor and he refuses to prescribe an alternative to the drug he already prescribed, then it is a very good idea to find yourself another doctor - not just for this matter, but a long-term doctor. You should always try and find an unbiased doctor, who wont try and prescribe stuff to you just because he got a cool gift from a drug-company, and one that will always be open to alternative treatments, such as MJ.

As for your Insomnia and anxiety.. I have no clue. Some people, such as myself, find that they cant get to sleep without smoking. I cant sleep for more than 2 hours without having smoked before-hand. Other people find that smoking alot actually causes Insomnia. My best advice is to smoke in moderation, ie, before you go to sleep. Try not to smoke too much, as this could worsen your problems. Also, smoking too much could worsen your anxiety as it speeds up your blood-rate.

Good luck