Initially, there is no milk in the breast of a pregnant female, but there is some colostrum. During the second stage of labour (the pushing bit) hormonal changes start to happen and the production of colostrum goes up. A couple of days after the baby is born the milk "comes in", round about the time that the "baby blues" comes on. The suckling of a baby on the colostrum stimulates this milk production. Thing is, the skin on the nipples isn't toughened much so any sensation of pleasure is obliterated by the red hot knives!!!
Once the milk comes in the baby feeds longer and longer at each feed and the skin of the nipples toughens. Also, the "let-down" reflex starts to kick in. This is when the milk glands and ducts within the breast are made to squeeze by the action of oxytocin. This same oxytocin, the release of which is stimulated by a suckling baby, also causes the uterus to have rhythmic contractions in the same way as when a female has an orgasm. It's Nature's way of helping the uterus get back to its pre-pregnancy shape and size.
The let-down reflex is an unpredictable little blighter. I only had to have water from the shower touch the skin on my breasts and I was squirting jets of milk onto the wall. It's fierce, not just a tiny twitch! Thing is, if a lactating female has an orgasm the let-down reflex will kick in and her partner can get an eyeful of milk - I kid you not! It's all down to the oxytocin, a physiological response. Some women have it in a much stronger form that others.
I breast fed my son for eleven months (I must be a bleeding masochist). Actually, I enjoyed it for the cuddly, nurturing, mothering feeling it gave me. I only stopped when he bit a small piece of my nipple off and lay back happily, chewing away.
I think that breastfeeding was designed by nature to be enjoyable, otherwise why would anyone volunteer for cracked nipples, unpredictable drenchings and a smell like three day old chewed grass? If you manage to get it right, you don't have any problems - so the best thing is to ignore the midwives and just let your baby get on with it - they know what to do. The prudes who think that a sexual sensation during breast feeding is perverted only demonstrate their ignorance of human physiology (note I didn't say psychology) and their own hang-ups and fetishes. On that note I remember breast feeding my son in a shopping centre. I couldn't find anywhere quiet so I had to sit in a cafe. A guy came up to me and called me a child abuser and pervert because my son was obviously too old to be breast fed. He was FOUR WEEKS OLD! The git even called security! Luckily they saw sense, but it was the last time I did it.