Realistic Calorie Goals.

So i was eating 1200 for a while - months on end and not losing weight, maintaining around 138 - 140 pounds (im 5 foot 5 or 165cm) so i upped my cals for the past 6 weeks up to about 1600-1700 a day, i have been bobbing up and down between 140 and 142 for 6 weeks. After first upping from 1200 - 1500 i gained 4 pounds almost immediately, then slowly lost 2 but when i eat too many carbs (*over 200 grams a day) i go back up to 142 pounds.

Does anyone have any advice for me on what cals to eat now, I want to lose around 15 pounds in weight - this is how my last few months have looked

Week beginning: Average Cals per day: Weight on last day of week

March 25th: 1234 Calories per day: 141 pounds
April 1st: 1305 calories per day: 141.9 pounds
April 8th: 1023 calories per day: 140.4 pounds
April 15th: 1216 calories per day: 140.2 pounds
April 22nd: 1383 calories per day: 139.7 pounds
April 29th: 1111 calories per day: 138 pounds
May 6th: 1221 calories per day: 138.8 pounds
May 13th: 991 calories per day: 138 pounds
May 20th: 1221 calories per day: 138 pounds
May 27th: 1300 calories per day: 138.4 pounds
June 3rd: 1460 calories per day: 141 pounds
June 10th: 1500 cals per day so far 142.6 pounds as of June 12th
June 17th: 1520 cals per day: 142.6 pounds
June 24th: 1715 calories per day: 142.2 pounds
July 1st: 1630 calories per day: 141.6 pounds
July 8th 1710 calories per day: 140.4 on Sunday morning - but on Monday morning July 15th 142,2 pounds

HELP PLEASE - any advice would be great, cos I am stumped with the above results! Thanks so much