hi, in your query, its my opinion its side effect of Etonogestrel implant : i.e. back pain
and mood disturbance, an weight gain are not a serious side effect, but Serious problems usually have warning signs. Tell your health care provider immediately if,
You have bleeding, pus, or increasing redness
, or pain at insertion site.
You have a new lump in your breast.
You have no period after having a period every month.
yellowing of the skin or eyes
You have unusually heavy or prolonged bleeding from your vagina.
The implant comes out or you have concerns about its location.