Blood in semen is a benign problem in most of cases and is know as Hemospermia. The most comm on cause is abstinence of sexual activity/ mastrubation for a long time. These are other causes and list is long , you can find that on web. The chunks you have mentioned are clotted blood and it will resolve with time. Few episodes over 10 to 15 days are normal and it resolves but if it persist for long then get an MRI pelvis to look for some cause. For burning sensation take some antibiotic for 8 to 10 days.
Dr Gautam Banga