this seems about right. When you participate in a contest, your rating will be adjusted depending on the rating those that placed above and below you had. if you hover around 1200-1400 I would assume you need to place in top 33-10% to increase your rating.
Also note that a year ago, noobs did not start at 1k rating but 1.5k rating. This means it is harder to increase your rating in the early stages now. Also, there is a cheating problem on code chef, this means that you will end your contest with cheater above you that have 1k rating.
The only part of your graph that I am perplexed about is the long contest where 23 people ranked above you, 4206 others ranked the same as you and 8228 ranked below you. This contest lost you 67 rating (1384 → 1317)
Now, What should I do to increase my ratings? I used to solve 2-3 problems in every contest. But from the last 5-6 contests. I either study at 3rd or 2nd problem because of exam and not visiting solving array questions. What should I do?
better to not participate