thank you for your query
chest pain on the left side can be due to numerous reasons.
a few of them are-
1.angina or cardiac pain
2. Chest muscle injury
3. muscle spasm due to excercise
4. Peptic ulcer
5. Pain from the digestive tract, such as esophageal reflux
6.gas due to constipation
from abdomen due to irritation of phrenic nerve
the red patch can be due to the bruising that develops after few days of injury.
i would advise you to start with muscle relaxants and hot compresses.
also get your B.P checked.it'll help you to narrow down the cause.
1.don't strain much
2.have regular food and sleep schedule
3.drink lots of water
wishing you good health