How likely is it to get pregnant while you have the birth control implant? also what effects do anti depressants have on nexplanon?

Unlikely: Hi! if your weight is not excessive, the chances of conceiving while using the Nexplanon are very small (less than 1%), antidepressants do not change the effectivenss of the medication. Weight gain can affect the "potency" though, so be careful. Dr brown.

No effect of SSRIs: The birth control implant (Implanon/Nexplanon) is extremely safe because it only releases the progestin, Etonogestrel. There is no estrogen and so the risk of clots is MUCH lower than any combined method. Failure rate is 0.05% in a year, which is almost better than getting your tubes tied. It is effective within a week of insertion and won't be affected by ANY antibiotics (except rifampin)/SSRIs.