14 months ttc how do you deal with every month bfn

After 14 months of ttc#1 each month that goes by and the constant bfns and Af arriving I don't know how much more I can take! I've spent all day crying after I have started spotting brown 3 days before af is due. I'm guessing af is now on its way. I seriously thought i was pregnant this month. Nausea, vivid dreams, exhausted, peeing non stop etc I even felt a sharp pain at 7dpo on my right side and thought I had implantation. Speaking to a fertility nurse at the moment and everything so far has come back clear! I just don't understand! Sorry to rant i just wanted know how to keep yourself positive after constant disappointment!