It is probably time to move on from leaded solder; it is still widely available and can be used in some applications but for most things, unleaded will do. If you are struggling, you might have more joy with a solder composition like 97.1, 2.6, 0.3 Sn, Ag, Cu, which is a eutectic alloy with a slightly lower melting point than the more common (and cheaper) 99C tin/copper alloys, so less prone to dry joints through movement during cooling, and pick a fairly active flux like Kristall 400 or 505.
A lot of the troubles with lead free solder are down to not hot enough iron - needs to be ~40-50C hotter, and selecting fluxes intended for low residues / no clean soldering of brand new, shiny clean, PCBs and parts.