3 months no period, chance im pregnant?

im 17, and not the healthiest in the world. i have always had an irregular period, but its been 3 months since my last but im showing no other pregnancy signs. no weight gain, no pudgeyness, i do have nausea, but im allergic to gluten and have been eating quite a bit of it lately. i am fairly fatigued, but was just diagnosed with fibromyalgia and the doctor linked the lethargy and sleepless nights to that. could there be a deeper problem as to why i havent gotten my period? or should i take pregnancy tests just in case??