Would a pregnancy test 45 days after intercourse be accurate? i have irregular cycles.

Depends: If you mean would it be positive if you conceived on or near that date=yes. The test relies on chemicals made by the implanted embryo/placental stalk. They reach detectable levels by 2-3 weeks after conception. If negative at 45 days out, no conception either occurred or survived. Sometimes conceptions do not implant but shed spontaneously.