How can i tell if i have a cold, allergies or the flu? i had sneezing, fatigue, muscle pains, no fever, nausea, headaches, & dizzy past for few days.

No fever: Lack of fever makes infectious process less likely. Rest, adequate hydration, and symptomatic treatment with decongestant / nonsedating antihistamine / NSAID can help improve the symptoms listed.

Cough ; congestion: Allergies often last longer and recur often. A cold does not recur and lasts for about a week or so. When you have this much coughing with nasal congestion and phlegm production, otc cold/sinus medication might relieve some of your symptoms. If it lasts for a long time, you have fever or produce colored phlegm, you should see a doctor. An allergist can sort this out for you.