What can I do to get a reply after an interview?

The USCIS is inconsistent in the amount of time it takes to make a final adjudication following an interview. Factors that may influence the amount of time include, for example, the type of application sought, delays relating to security background checks, the USCIS office handling the case, retrogression of Priority Dates, and complications or other special issues relating to the specific applicant and application. When an applicant is represented by an immigration attorney, that attorney not only is able to assess likely reasons for delays and steps that can be taken to reduce or eliminate delays, but also is able to use the formal Liaison Process between the USCIS and the American Immigration Lawyers Association to try to prod the USCIS to complete a delayed adjudication.

You should be getting a reply, however, you forgot to tell us why you had the interview: in connection with which application. it is important to know because after some interviews, the officers would give you their decision right then and there, and in different situations, it may take several months (ex. asylum cases).