Is it normal for my baby's sleep pattern to get good and then get bad again?

Yes. Many events can cause a disruption in baby's sleep pattern. Even "good sleepers" can have a temporary set back after vacations, illnesses, or major changes in routine. There are also several developmental stages which can be associated with sleep disruption, such as separation anxiety around 9 months of age.
Teething. When a child begins to teeth he may be in pain and wake up during the night.
Yes. A baby's sleep pattern may be affected by illness, colick, travel, etc. If you are having a hard time getting the baby to sleep though the night your pediatrician can recommend stategies. Most will sleep through the night by 2-3 months of age. Don't allow a baby to sleep more than 4 hours at a time during the day or they may get their days and nights mixed up!