What Causes Elevated TSH Levels?
Thyroid
Detailed Answer:
To the best of my knowledge there is no published medical literature that suggests any impact of marijuana on the thyroid.
What you most likely have is a condition called Primary Acquired Subclinical/mild Hypothyroidism. In simple language, this means that your thyroid gland is not producing enough hormone and so your pituitary has to increase its secretion of TSH in order to stimulate the thyroid to produce more thyroid hormone.
When I see someone like you in my practice, in addition to a thorough physical examination especially to look for a neck swelling (goiter = thyroid enlargement) I tend to order:
CBC
Thyroid auto antibodies (anti TPO and anti Thyroglobulin)
Liver and kidney function tests/Electrolytes, Glucose, Calcium
The antibodies, if positive, tend to suggest that you will likely need medication to treat your condition particularly if your TSH remains persistently high.
However there is a condition called Thyroiditis in which the TSH may appear on the higher side during the normal course of recovery. This does not require any treatment. So checking in a couple months is reasonable idea.