What causes severe fresh bleeding (painless) from rectum for a short period?

[STYLES80]

I had severe case of bloody diarrhea (mostly fresh blood without any stool without any pain at all) on 28, 29 and 30 April I had this for 8 to 9 times and then it stopped on third day just like it started, I took antibiotics for 7 days, My haemoglobin dropped from 14.5 to 8.2 in 5 days, for a while I felt dizziness, near fainting and weakness, I got blood transfusion one bag.
Its been over a month it didn't happen again and finally I have started to feel good again now hemoglobin is 10.8 and in recent stool test there is no blood or diarrhea.
I was asked to got colonoscopy done but since I'm too afraid so far I didn't get it done and still there is no sure diagnosis of what caused it.
One doctor said it was accute infection which stopped upon taking antibiotics and that I should monitor weight changes and get blood test done once a month to be sure.
I want to know what can cause this massive bleeding over 3 days with no prior experience of any sort of pain or fever or any other symptom.
5 months taking I was took whey protiens and pre workout supplements in high doseses for about 2 months and it immediately caused loss of appetite could that be linked to this problem?

[specialmom]

Well, the idea of an acute infection has been told to you and it could have been that.  The reason to do a colonoscopy is to see if there are any abnormalities such as polyps or issues that would have caused this type of bleeding.  Ulcerative colitis can cause this bleeding, ulcers in the anus and colon, essentially.  This can be chronic like IBS or acute.  I think the colonoscopy is essential here not because you likely have anything scary going on but as preventative to make sure this doesn't happen again.  Don't be afraid of taking care of your health as that will just make things worse down the road.  good luck

[STYLES80]

Thank You for your advice, I have a colonoscopy scheduled for tomorrow lets hope everything goes fine

[NanaRuth410]

I have heard from a person who has researched this issue. A colonoscopy can cause problems if your over 60. If it is for no reason than a minute bit of blood found in your stool. After the procedure you can have more problems and infections. Remember do what you feel is right. Your Doctor can't force you to do any procedure. God Bless you

[STYLES80]

I am 27 years old