Sponge rods, flex rods, pin curls... Depending on the length, sock bun curls are GORGEOUS. (And easy!)

If the blood tests came out with normal thyroid and hormone levels, etc, then you could try supplements to be sure it isn't nutrition based. I don't know who you saw, but you might consider seeing an endocrinologist instead of a GP. They'd be more likely to identify a problem.

There are some people who have straight hair and their pregnancy turns it into curls that stick around after delivery, and the opposite can happen, as well. :/ I would try protein treatments, lots of good moisture, LI, oils, and scrunching in some gel. See if any of that helps with your frizz issues. It would also help to identify the source of your frizz.
2c/3a/3b, Fine/med, Dense, high porous, & normal elas.

Lo-poo - Renpure Keratin, SMR, Giovanni SaS
clarifying - mix Johnson's H2T with low poo
Co-wash - Suave Nats. clar. or coco.
RO - GVPCB, Ion Eff. Care, TN.
LI - SMR, Cure Care, or RO
Seal - MO or Jojoba
DT - + honey, ACV, & EVOO to SM masque & GVPCB
PT - Gelatin!, CNPF
Styling - FSG, AIF, BRHG, LALS/PS, GF curl spray gel, SM Souffle/Smoothie, LOOB
Oils - MO!, EVOO, jojoba, GSO, SM Elixer, EVCO, VO5 Hairdressing