What Causes Pain During Urination After Having An Intercourse?

I am trying for a baby and since having sex the other night I am now suffering with terrible pains at the end of urinating not during. I drink a lot anyway so don't feel I'm going more often but less is coming out... I noticed some light blood when wiping which comes from my vaginal opening rather than urine itself which is slightly darker than normal any ideas please? Oh I started taking a sachet of Cranberry for infections (one so far) and pain has slightly eased already. Any help would be appreciated :)