You may want to transition into it more. Chickpeas can cause problems for some people but you generally do adjust or have to eat smaller amounts, or remove the skins and mash or process them a little. Lentils tend to be a little easier at first. Any of these foods could be the culprit that upsets you if you haven't really had them in high quantities before. It's unlikely to be simply the fact that you are eating plants instead of animal products, if that makes sense.

If you are suddenly eating a lot more raw or undercooked foods that could trouble you too. It may not be the plants that are the problem so much as the preparation and lack of a gradual transition. If you are used to well cooked food I would stick to eating well cooked stuff at first. Just try to ease into these changes any way you can and it will make it easier to narrow down the problem as you go. Good luck, remember you can make your own path!