Hi, i have a lump on my vaginal labia majora...

What is the possible causes of your medical condition ?
according to the mentioned info in your consultation , your test were normal , which only lead to only possible cause which is bacterial infection ( Infections of hair follicles ) 
- period isnt a cause in this case , but it may be a trigger 
What is the possible treatment in this case ?
treatment options are topical which mainly includes :
1. topical antibiotic such as : clindamycin 
2. topical vaginal wash 
3. you can also use neomycin 
* all should be used 3 times a day till its gone 
General advices :
1. shave the pubic hair around ( use only shaving machine 
2. Paying attention to personal hygiene 
3. Avoid tight and non cotton underwears 
4. Avoid using deodorants and products that contain perfumes and  irritants 

first of all you must continue all the specific cousrse 
 and if the medical treatment not going well you can go to the surgical treatment
and the surgeon can take the swelling or abscess  and send it to the pathological laboratory to   decide the type of this is bacterial infection