I do not think that you are constipated - how can you be constipated if you go every day LOL ! ?! In my humble opinion - what is happening is that since your fissure hurts so much now (unlike when you were healed for 6 months) , your anus and sphincter spasm to the max - can not relax reflexively due to the extreme pain. When you sing you relax it somewhat (again subconsciously) and drinking or eating anything starts peristalsis of the GI- reflexive reaction again that is controlled by peripheral nervous system. Coffee is also stimulant - initiates peristalses.
Of course you are holding breath - it is again reflex reaction to the pain. That is what women do when they give birth - stop breathing and that is why LaMaze is so helpful and "breathing over contractions". It helps relax muscles and also helps dealing with pain since one has to concentrate on something elese - counting and breathing.
To make the story short - if your anus was healthy, you would not feel the tip - no matter what consistency it was. I can almost bet that it is not "hard tip" - it is normal tip that your fissure registers as a "rock" since it gets stretched and hurts like hell : (((.
So it is vicious cycle - pain causes sphincter to clench - clenching makes poop go slowly out - going out poop makes fissure to stretch - it hurts even more - pooping is over - sphincter after the shock stays in the permanent spasm - that equals pain for hours , even whole day.
Try to use some laxatives and stool softeners even though you are not constipated - just to make your poop ultra soft and playable until you have your LIS and relax that sucker forever !!!!!
Best of luck and I hope my theory made sense for you
