I know it sounds silly but, make sure the CB isn't switched to PA mode, undo the mic, unscrew the the two screws holding the mic connector together, and see if all the connections have a good solder joint, if not resolder them, or if you're not very good at soldering get a mate to do it.
you should not get a mate to park too close to you and key the mic, as you might damage the signal meter if too close.
but if your mate was right next to you, and he couldn't hear you, it's either mic, or the CB is knackered.
just make sure you never keyed the mic with no antenna connected, as this can also damage a CB
SWR'ing a Cb means you need to match/tune the Antenna to the CB you are using, ideally it needs to be the lowest you can achieve 1.5 max, but ideally be lower, you need an SWR meter to do this, in the old days, this was a requirement of the license it cuts down the interference you give off the transmission to things like televisions ect.
it still is a requirement, even though there is no license now, the rules still apply