Well, you aren't used to the activity and your body reacted. Friction causes swelling. It will go down but you need to ask the other person to be more gentle. Clearly they probably don't know what they are doing. You have to be vocal as it probably felt alright but not great. But either way, the swelling is a reaction to the friction. The swelling is not a disease or from a disease. You can get an std from oral sex but not if the other person has never had sex before or done it before. Fingering is very low risk for anything. This isn't due to an std, just your body reacting to the activity. You can try an ice pack and/or ibuprofen. good luck