I wouldn't take a break, that is probably the last thing you want to do right now and pretty bad advice. You're currently doing a fairly low number of reps per week.
It sounds like you might not be pushing yourself hard enough to increase your rep range. Its easy to fall into a rut and not hit it as hard as you can everyday in the gym. I would up your reps per week dramatically. If you can, get to a bar at least everyday, maybe multiple times a day which would be ideal. Shoot for 50-100 per day of you can get there.
And lets be honest, you can probably hold on to the bar after that 7th rep, and crank out another. After a year, you should have sufficient grip strength. Just hang on the bar after your last rep and crank out another, even if that rep is slow and ugly. Do this with every set. Get fixated on the number 8. If you really push yourself, I bet you can get it pretty easily.
Practice different grips too. Personally I dont like the supinated grip pullup because its easier, is basically a curl exercise, and will trash your elbows if you do it a lot. I like the pronated grip, as wide as possible.
I highly recommend this program;
http://www.strongfirst.com/the-fighter-p...revisited/
You can see here that the program relies mostly on consistency of daily reps, and slowly increasing your rep range. If you complete this I guarentee you will be busting out 10 - 12 rep maxes, or more.
The 5RM Fighter Pullup Program
Day 1 5, 4, 3, 2, 1
Day 2 5, 4, 3, 2, 2
Day 3 5, 4, 3, 3, 2
Day 4 5, 4, 4, 3, 2
Day 5 5, 5, 4, 3, 2
Day 6 off
Day 7 6, 5, 4, 3, 2
Day 8 6, 5, 4, 3, 3
Day 9 6, 5, 4, 4, 3
Day 10 6, 5, 5, 4, 3
Day 11 6, 6, 5, 4, 3
Day 12 off
Day 13 7, 6, 5, 4, 3
Day 14 7, 6, 5, 4, 4
Day 15 7, 6, 5, 5, 4
Day 16 7, 6, 6, 5, 4
Day 17 7, 7, 6, 5, 4
Day 18 off
Day 19 8, 7, 6, 5, 4
Day 20 8, 7, 6, 5, 5
Day 21 8, 7, 6, 6, 5
Day 22 8, 7, 7, 6, 5
Day 23 8, 8, 7, 6, 5
Day 24 off
Day 25 9, 8, 7, 6, 5
Day 26 9, 8, 7, 6, 6
Day 27 9, 8, 7, 7, 6
Day 28 9, 8, 8, 7, 6
Day 29 9, 9, 8, 7, 6
Day 30 off
You start with an all-out set and then cut a rep in each consecutive set for a total of five sets. The next day add a rep to the last set. Then a rep to the set before that, etc. The system is intended to be used for four weeks. In the end of the month take two or three days off and then test yourself. It is not unusual to up the reps 2.5-3 times. In other words, you are likely to end up cranking out 12-15 reps if you started with 5. If you can already do between 6 and 12 reps start the program with the first day your PR shows up. For instance, if your max is 6 pullups start with Day 7; if your max is 8 start with Day 19.
If you run into a snag with this routine, back off a week and build up again. If you hit the wall again switch to another routine.