Generally speaking, prolactin levels and secretion from the anterior pituitary are going to be in flux in a female human on a daily scale and also monthly if the woman has a regular cycle. Prolactin has many different effects in the human female body with the most well-known effect being enlargement of mammary gland during pregnancy in preparation for increased milk production. Since you are blocking prolactin levels and prolactin decreases levels of estrogen/testosterone in the body, it makes sense that you see increased libido/better mood. In terms of negative side effects, I suppose you "might" see some breast atrophy however, since your decreased prolactin is caused by medicine and not some underlying medical condition, you might not see any negative side effects.
So to answer your question succinctly, if you are past puberty and are not pregnant, you probably won't see any negative side effects if the dose you're on is on the low side.