You should finish what you are taking now, then allow adequate time to completely recover before starting the test cycle. Provided proper diet, great gains can be made with test only, you would need to propose what dosage and timeline you are considering before we could advise further. If you're not sure what dosage you want to take, a good starter cycle is 500mg/week for 12 weeks, and split the dosage into 2 shots of 250mg per week.
Make sure you read up on pct as it is as important as the cycle itself, and make sure your diet is sufficient to grow.