As an evergreen, it is natural for Pineapple Guava to lose some foliage, if it is last year's leaves. If this year's new leaves are shedding, dig into the soil to confirm moisture levels. What fertilizer did you use and how much new growth (branch length) has occured?

Feijoa is a lot less fussy than the more tropical guavas. Once established, the shrub (or tree if shaped) is drought-resistant and will do less well if over-watered. Here in S. and C. Calif. we don't fertilize pineapple guavas very often. As with figs, too much nitrogren will give you lots of leaves and less fruit.

You should be tipping branches to force laterals; the fruit appears on new growth. Remember, the flower petals are delicious and sweet. You can carefully remove them to eat and still expect fruit to develop if you don't disturb the rest of the flower.