The Drunken Weed by ED Robson

Humor, romance and adventure as Gesh, the Drunken Weed, a Mesopotamian Goddess and her (unknown to him) brother-in-law, John, the Irrelevant One, a call centre worker, embark on a time travel adventure across the multiverse following her unsuccessful attempt to assassinate him.
Along the way they meet Greek and Norse gods, Roman invaders, Neanderthals, a druid and an Anglo-Saxon shield maiden among others. Gesh discovers an identical version of herself on an alternative Mars and gives birth to twins while John marries a second wife (unbeknown to his first), Gesh’s best friend, Pandora of Greek myth fame in Napoleonic England.
The first book of the light hearted 'Irrelevant One Saga’.