Missed Period Post Sex. Had Experienced Severe Cramps With Anal Pain Causing Difficulty In Sitting During Periods Due. What Could It Be?

Hi, I am a bit confused right now to whether I am pregnant. I had sex 3 weeks ago and I have regular periods. However, this is the first time that I have not had my period this whole month. I am hoping I will have my period soon but if I do it ll mean I missed my period for a whole month and my period would of run into the next month. I don t know if that matters a lot but as you can tell I m a bit confused by this. Last week I was expecting my period as I experienced very extreme cramps . I do tend to sometimes experience very bad cramps, but last week it was awful because I couldn t move easily and I also experienced pain up my anus which made it very uncomfortable to sit down on that particular area. I looked this up on the web and many people said that this was due to period pains. A week later I am still waiting for my period but have not experienced any more cramps since that very painful one. I am getting worried now and am thinking of taking a pregnancy test and going to see a doctor, even though I am very nervous to do so. If anyone could give me some advice on this and what to do next as I don t want to be pregnant I would really appreciate it.