weight loss/thyroid issues?

my mom and i have been dieting and working out 5-6 days a week for the past few months, she is losing weight regularly, and i can not seems to lose more than a few pounds and then i gain it right back. my grandma, my mom, and my aunt all have thyroid problems, and are on medication to control it, i have never been tested for thyroid problems (im 23), my mom keeps telling me i need to be tested, could a thyroid problem really stop me from losing weight? i always felt like saying that was a cop out for people who werent really trying hard to lose weight but i am really trying hard, my mom and i are doing the exact same workout routine, and eat a lot of the same things too, so im just confused as to why shes losing weight and im not, could it really be due to a thyroid issue? thanks for any thoughts!