Thanks for the very clear history and photographs. The red rash looks like a bruise and this is likely to be due to excessive pressure over the area, aggravated by the compression from the stripes which squeezes the enclosed areas. This will typically take 1 to 2 weeks to resolve.
Blood tests are usually done to rule out underlying conditions like low platelets which may lead to increased susceptibilty to bleeding. I assume these tests were done and were normal.
I would suggest wearing leotards without this stripe pattern so that there will not be added pressure to the skin. Hopefully, you will not get this again with the change in attire.
