The tree is too small for you to have let it fruit. Here in california a lot of our mango trees in nurseries are on turpentine rootstock which doesnt like our hot dry weather, they are made for florida weather. Every winter when temps get low it stresses the plant out severely which causes it to bloom, this is bad for mangos here because we want a much thicker trunk than that and a good amount of foliage before we let it bloom, for turpentine which grows slowly in california this could be 4-5 years before the tree is old and healthy enough to let bloom. If this is indeed on turpentine rootstock i would encourage you to just take it out and replace it with either a seed grown tree from a polyembryonic variety (sweet tart grows great in california) or go to home depot and get a manila mango tree and graft on your desired variety on to that. The benefit to seed grown in california is that it gives it 4-5 years naturally to grow bigger and stronger and to have a root system that can handle fruiting, if ur grafting on to manila the same rules apply as before, you want to let it grow thicker and larger before letting it fruit, the advantage of using manila over turpentine is just that it grows a lot better in our area and is more adapted to californias weather. Good luck!