hi might be teething. my first got her bottoms and i didnt even realize it till after they were up, but the tops bothered her. i wouldnt think its the vitamins(although if eating healthy and breastfeeding, he really doesnt need them) but you may want to change the time just in case.
but also have you considered "baby led weaning". you can google it. the idea is babies will not swallow food on their own until they are ready due to a reflex. when the reflex is gone, and the baby has the pincer grasp, there is no reason he cant eat nutritious fresh foods. it sound like he wants to do it himself. try cutting a banana in pieces, not little bitty pieces, but more like where he can hold it and chew on it. he should be able to gum it just fine(i know several people whose babies didnt have teeth at one but of course they fed them real food). well cooked broccoli stalks so he can hold the stem part and carrot sticks. avocado and sweet potatoe are very good for you, the baby will mush it but then eat off his hands. it is messy, but then your baby can do it himself, and will be eating fresher foods. my daughter is EBF and has just started solids eating avocado, bananas, and apple. didnt seem to live peach.
its just something to think about. there is a lot of info on mothering.com and la leches website in the forum "starting solids". good luck