First off, this came in as a pregnancy question, so I am going to assume you are pregnant, and that you have already had an ultrasound showing that the pregnancy is in the uterus and not an ectopic. Severe lower abdominal pain caused by a tubal pregnancy requires urgent medical attention. And of course, anyone hearing that you are having right lower abdominal pain might also note that the appendix is located in that region. Abdominal pain that is associated with fever, feeling ill, or severe pain should always be brought to the attention of your medical team, to be sure nothing more serious is brewing.
Now we can move on to the more likely causes! Constipation, gas, and bloating are really common in pregnancy, caused by the pregnancy hormone progesterone, and by the mechanics of the growing uterus blocking movement through the intestines. Constipation is but one of many annoyances that can accompany normal pregnancy.
Is it possible that you are so constipated that when you added in the fiber laxative (be it Metamucil®, Citrucel®, or Benefiber®) it may actually have made things worse, as pressure built up behind the blockage? I have started to think of fiber laxatives as preventive measures for constipation, rather than treatment. Once you are very constipated, you need the “big guns” to empty out, so you don’t add bulk behind a blockage. Milk of Magnesia® is a good first line, although short term use of Senecot® is also OK. Once you are “cleaned out,” taking a fiber supplement and drinking lots of fluids every day can help keep things moving. Of course you should talk to your doctor or midwife to get personalized medical advice. Good luck!