I am sorry to hear of your pain, and hopefully I can offer you some advice and guidance. A hernia is when the intestines form a bulge or an outpocketing...and you are correct in that heavy lifting can be a cause of them. The hernia doesnt let the intestinal contents pass through the GI tract as you fear, and so that by itself wont make the cut on your anus worse. However, there are concerns that present with a hernia. IF the hernia was to become strangulated, that is to say if the blood supply to it is cut off by stool or the tissue itself pressed upon itself. The bowel can die, and that is a true medical emergency.
Hernias need to be examined by your provider. If it is reducable, it still needs to be repaired, but some providers will elect to monitor it instead, depending upon its size. If it can NOT be reduced, it absolutely has to be repaired, or else it CAN become strangulated. A hernia that strangulates usually causes intense pain in the hernia followed by marked tenderness. Because of the intestinal obstruction, there is abdominal pain and vomiting.
Here is a useful website on Hernias: www.emedicinehealth.com/hernia/article_em.htm
Now to your other issue: the anal tear. I am not there, so cant state with 100% certainty that this is what you have, but from what you describe, it could be an Anal Fissure. This is actually common in children and infants, but happens as well to adults. Normally they heal on their own, but as you have experienced, at times they do not. It is these times that they do not that they need medical attention. If they last too long...over 6 weeks...they can become chronic, and that means you will have them repeatedly. Repair of this is by surgery.
You should be seen by your provider as you have had this for three weeks and have intense pain after a bowel movement. The acid feeling you feel is likely your stool as it CAN be acidic, and it IS irritating the cut anus. Those are two signs that you need some outside help to heal this...the fact you have had this for 3 weeks and your intense pain. Your provider as well will look for things that may have caused the anal fissure...irritable bowel diseases can make the anus prone to tear as the anal and intestinal tissue changes due to the disease.
You are doing the right thing by keeping your stools soft. You can also take a sitz bath...essentially soacking your buttucks in warm water. That will make you feel better and improve blood flow to the area. Exersize also helps improve both tone and blood flow. You can also use Preparation H to ease the discomfort.
Here is a useful website on anal fissures: www.mayoclinic.com/health/anal-fissure/DS00762/DSECTION=1
In both cases...your hernia and your potential anal fissure, you need to be evaluated and treated by your provider, and I urge you to do so as soon as you can.
I hope I was able to help and if you have any other questions please ask.