Don't worry!!! There are MANY people out there that struggle with these. But all is not lost. There are options for you to use. Both of which will suffice in helping you to achieve a multiple rep pull-up goal!!
A: Unweight yourself - Drape a resistance band over a pull-up bar. Step inside the band and this should help with unweighting your bodyweight, making the job of executing the pull-up easier. Depending on the resistance of the band, you may need to use a couple.
B: Inverted row - This is the easier version of a pull-up itself. Only difference is the angle of pull, but the concepts are the same! You're still needing to PULL yourself up against gravity. Become proficient here and it will only help you further in performing normal pull-ups. You can make the exercise harder (or easier) by the placement of your feet. Bring your feet in and the exercise becomes easier. Kick them out fully and the inverted row will be more difficult. Added benefit: Improving grip strength!!