Chronic stress, poor posture, and repetitive motions can cause muscle fibers to stick to each other and become adhered. This new hard and lumpy feeling is a muscle 'knot' or adhesion. Adhesions are incredibly common but common doesn't mean they are normal or harmless.
Adhesions happen when we spend too long sitting at computers, having poor posture, and even tension from daily stresses.
You can work on these knots at home using various techniques. One of my favorites is using hydrotherapy in the form of a vascular flush. Vascular flushing utilizes both cold and hot to increase circulation and relax the muscle. If you want to try this treatment at home, all you need is an ice pack and heating pad (or better yet try it in the shower!). Always start and end with the cold, a typical cycle may look like 3 min cold, 1 min hot, repeat 3-4 times, ending with 3 min of cold.
Other handy ways of work these out at home include myofascial release, self massage, or an epsom salt bath soak. Don't forget to add daily stretches into your routine and check your posture often. If your shoulders are hurting, which is often the case for many people, you may need to stretch out your chest muscles and focus on bringing your shoulders back and down.