Thanks a lot for your question and concern. Certain blood examinations need to be carried out for verifying whether the infection has spread further or its at the preliminary stage. Depending on the severity & type of sexually transmitted disease, proper medication can be advised for you. Certain Sexually transmitted diseases which spread during anal & oral sex are: Venerable diseases like VD, HIV. This infection can spread to uterus & fallopian tubes if not given timely medication. This condition is called pelvic inflammatory disease caused by bacterial infection. Well the medication does give relief to a great extent and also prevents further spread for such infections, it is advised to have a safe sexual intercourse with your partner.
In order to reduce the ache & distress, you can wear cotton stuff which may not cause further rashes. Luke warm water is also recommended for you while taking a shower. In case your blisters grow further, you should immediately consult a doctor for antiobiotic medication. Care also needs to be taken while having a sexual intercourse with your partner. The regular medication as well as application of the lotion can help a great deal in healing of the blisters as early as possible. Good Luck.