I gained 10 lbs in 3.5-4 weeks. I don’t believe I changed much about myself. I do have hypothyroid that am on medicine for. Could that be cause?

Weight change. It could be many things, but thyroid dysfunction is a common cause of weight change. Since you have already been diagnosed with hypothyroidism, this is where I would start first. Definitely get some labs done (including, of course, thyroid labs). Perhaps your medication simply needs to be adjusted. I hope this helps. .
Weight gain causes. I understand your concern.
Hypothyroidism does cause weight gain.
Other possible causes are:
• Anti-depressant medications
Fluid Retention
Blood pressure medications
Diabetes medications
Please see an Endocrinologist for medical causes
and a Psychiatrist for stresses in your life causing Depression.
Your Health is Precious!