This type of behavior, and variations of it, is relatively common with nursing toddlers. At this age your baby should be ready to learn some reasonable limits and accept loving guidance toward more acceptable and comfortable behavior. You may want to begin by holding your baby's hand to prevent him from pinching or playing with your clothes. Sometimes this is successful if you play with your baby's hand or kiss it to provide a more acceptable activity while also acting as a gentle physically restraint. Some mothers find that talking to their baby, or singing, helps to hold his attention and lessens the fidgeting.
Some mothers use special necklaces that are made just for the nosy or distracted nursing toddler.
The necklaces are made with a sturdy string or cord and large colorful or toy-shaped beads that the baby can play with during nursing, instead of playing with mom's nipple or other body parts. If you opt to try the necklace, make sure it is made with non-toxic and safe materials. Some have also had success with giving their baby something else to hold on to, and play with, such as a small stuffed animal or blanket. One advantage with a stuffed toy or blanket is that can be used as a transitional item to help the baby settle when you are not available, since your baby will associate the special breastfeeding toy with being comforted. You may also have success by nursing in a more quiet environment, when you can, and wearing a bra that does not give easy access to your other nipple.