My big toe nail is yellow with a line straight across it , is this fungus and how can i treat it?

Possibly fungal: Need a photo as too many causes of nail discoloration. If onychomycosis(nail fungus), it must be treated by an oral medication for 12 weeks as the dermatophyte is embedded in the nail and mudt be treated as the nail grows. Also, the medication is occasionally damaging to the k=liver and must be monitored by blood tests of liver function. Visual and touch exam by an internist should be done.

Manual treatment: Toe nail fungus also responds better to the medication of the nail plate is ground down and trimmed, to manually remove the fungal debris. This reduces the chances of getting it reinfected by fungus and it also gives immediate improvement in appearance. The line across the nail might indicate a new nail plate growing in underneath.