Did you make an ordered factor, like this:
library(ggplot2)
library(dplyr)
#>
#> Attaching package: 'dplyr'
#> The following objects are masked from 'package:stats':
#>
#> filter, lag
#> The following objects are masked from 'package:base':
#>
#> intersect, setdiff, setequal, union
df <- data.frame(Month = c("Jan", "Apr", "Jul", "Oct"), Value = 1:4)
ggplot(df, aes(Month, Value)) + geom_point()

df <- df %>% mutate(Month = factor(Month, levels = c("Jan", "Apr", "Jul", "Oct"),
ordered = TRUE))
ggplot(df, aes(Month, Value)) + geom_point()

Created on 2019-05-22 by the reprex package (v0.2.1)