The Handbook of Chemistry and Physics has a table of the solubility of
silver nitrate. According to it, you could have up to a 40% solution! 10%
by weight would be 10 g of silver nitrate per 100 g of water (or,
essentially, 100 ml of water). Thorough mixing may be necessary - rocking
(inverting) the closed container several times should help. Maybe there is
some impurity in your solid silver nitrate. If that is the case you might
want to let the solid settle and decant the liquid into another container.
Use a brown bottle, of course, because of the light sensitivity.