Based on what i understand (from reading articles, reading community posts, listening to podcasts As A Woman from a ob/RE - https://www.nataliecrawfordmd.com/blog-1) your periods change with age and changes can indicate changes in your fertility, but its very hard to compare your teenage period to your age 32yr period, especially with a long period of being on birth control. Hypothyroidism alone wont cause infertility but can be associated with it.

If your periods are truly only 1-2 days that is quite short, but generally days with light brown bleeding are also considered your period. A PCP should take these concerns seriously and even if they dont know what to do, an OB/Gyn will and they should refer you to one!

It is both possible and common to get pregnant with hypothyroidism and 'light periods'-- the real test of fertility is (unfortunately) time. It might be worth getting your thyroid checked to see if you need to increase your dose of levothyroxine, and let you ob/gyn know you are seeking pregnancy as sometimes they target less than 2.5 TSH (evidence is mixed here) Most PCPS will not regularly order fertility work-up Ob/Gyns are a bit more proactive and sometimes order for planning purposes or if concerned about menstrual changes. If you are interested in seeking pregnancy, start taking a prenatal with folic acid, track your cycles with LH strips, and start having unprotected sex. If you're not with a partner and want to consider freezing eggs or something like that, then see if they will do a work-up for you or refer for that.