Need to train effectively without huge distances

This is most likely a topic for training but I need some general advice also. I will be 60 at the nationals and swim both BF and FS. I go a 27.66 in the 50 BF, and a 25.29 in the 50 FS. For the 100's it is a 1:03 in the BF and :56 in the FS. I lift 3x/wk and swim 4x/wk. For the most part I train alone. I find if I go much more than 2600 yds in a workout I am close to killing my shoulders. I also should note that even in practice when working on 50's if I go increments faster than 1:15 I can only do about 6 FS. If I am working on BF I need to do the increments at least around 1:30 and then I can only do around 4 of those. If I swim a 100 BF I am about done for the day! My times have been coming down every year but I think if I could get more out of practice I would see much more improvement. A normal workout for me is: 400 warm-up 4X 100 stoke on the 2:30 5 x 100 broken with 10 sec rest on 1st 25 and 1st 50 on 4min 8 x50 stroke on 1:30 400 kick (3) 4x25 on 45sec 200 cool down I have followed a lot of the threads and looked at workouts but am searching for something I can do without breaking down--another possibility is that i am just lazy--not sure how to fix that!