Yes, for starters leave out the lemon juice. Not sure where you heard that putting lemon juice in your solution was a good idea, it isn't. Not that it's going to harm you, it won't, but it will aggravate it to some degree.
Often times when a person evacuates, the stool is a tad harder than it should be, and when this happens it causes little micro-cuts. Sometimes when we pass hard stool you see blood, this is partly the reason. Now, I don't know about you, but I have gotten lemon juice in an open cut before and it hurts. Same thing is going to happen down there as well.
I often am bound up and require enemas for medical reasons. I am usually also in a constant state of dehydration as well which also causes harder stool than I would like. So, when I would take an enema, it would force me to evacuate quicker than I normally would causing these micro-cuts. Then I would have the same problem as you.
So let me see if I can explain a little better here. You have these micro-cuts already due to your earlier evacuation. Then later you have anal sex. Now, the cuts are already there, so when you have anal sex you just irritate and make the cuts larger than they already are. It's sort of like re-opening a wound, and because the tissue is already weak, it's going to tear more and irritate more quickly.
So, long story short here, a few things you can do.
1) Drink more
2) Take enemas more often
3) Leave out the lemon juice, just use plain warm water
4) Try a little anal massage prior to your enema to help loosen and relax you backside. That will make your evacuation a little easier.
Hope this helps some.