Could i have lymphoma? bad headaches for few weeks, small lump behind ear (firm but moves slightly), tiredness and breathlessness?

Have it checked out: Sounds like a small lymph node, which for a 19 year old is most likely completely normal. However, if you are having other symptoms and are concerned for a cancerous process, have it checked out. The bump may or may not be related to your other symptoms.

Symptoms: Your symptoms are nonspecific and only suggestive that you should see a doc to be evaluated.

Yes, but...: There are more common things that are probably the cause for your symptoms. You may have a viral illness, an infection, or a different problem. Go see a healthcare provider for a check-up. Some simple blood tests may help figure this out. The small lump behind your ear could be a lymph node, but these get enlarged with many viral infections, not just lymphoma.