Yeah.... i also experienced same thing as you.. Last season i won the leage with perfect 26-0-0 score and +110 GD
This time also i didnt make any great changes except adding 2-3 new players to my starting XI and in first half of the season i was at 10th position , then i changed some orders and tactics and bought some more new players and replaced them with under-performing players in starting XI and atlast i managed to secure 4th position , finally !! I was fearing worst of getting below 7th pos. , but thanks to late wins (Won 4 out of last 5 matches and drew 1 )
Overall i finished fourth with just 14wins (compared to last season's 26)
Hope it would not be the same next season also :/

P.S :- i also experienced a lot of injuries this season( big ones 5days+) compared to last season ( 500% more)
In first half of the season , i had like 1 injury per match or my best player would get his second yellow card just before some imp. match and he is banned for 1 match
Though last seven matches i had only 2 injuries (small ones)