Hello,
It is not recommended that you continue to take tetracyclines if you wish to become pregnant.
A short course of topical medications such as benzoyl peroixide or reti noic acidgel is recommended.
There are certain other blood tests such as
complete blood count, Vit B12 levels, Ferritin levels, Antinuclear antibody,
TSH that can help understand why you are losing hair.
Please stop taking antibiotics if you wish to get pregnant.
Best Wishes.