Can breastfeeding affect your cycle?

My son is 21 months old now and I still breastfeed him. I started getting a period last November and since then every couple of months my period will come a few days late. Like this month it was 6 days late, last month it was 4 days late, and in March it was one week late. I have been trying to get pregnant since April but have been unsuccessful. This month I really thought I must have conceived because we tried every other day for a week while I was pretty sure I must be ovulating (I always get discharge when I'm ovulating, but this month it didn't get real thick like it usually does, but it did last several days). Then right around the time my period was due I noticed thick discharge for a couple days but didn't really think anything about it. Then my period started two days ago and I was kinda surprised I didn't get pregnant. Could breastfeeding be messing up my cycles?