About me - 40y/o female, healthy, vegetarian, exercise regularly, normal weight/BMI, no prescriptions or other medical conditions.

I discovered low thyroid around 33y/o with fatigue and dizzy spells. GP ran blood found T3 low but not T4 (or vice versa) and prescribed Armour. Continued on it for about 3 years and eventually phased off it for no particular reason. Have felt good/great for a few years without it, until I started experiencing hypo symptoms again recently. OB/GYN did blood and hormones and determined a was on the low end of normal for one of the thyroid hormones. Seeing GP this week with blood results, but discovered that Armour is no longer available. What is a good alternative? Do I need to take Calcium or other supplements on thyroid meds? Should I be aware of any side effects?
Thanks!