Error in Opencart 1.5.6.1 - Website Not Loading

My website was hosted on shared server. Server owner told me that my script was consuming lot of resources. I thought it happened due to traffic on my website. I shifted to another shared hosting where I hosted only single domain. There also I was told that website consuming lot of resources. Then I moved to VPS server. Now they told me that my script is generating n number of MySQL queries like creating products, submitting product_to_category and so on. They told me that even if your website has no visitors your script keep on generating MySQL queries all the time. They suggested me to see Error Logs and resolve the issue. Otherwise Error will continue. My website does not load and gives 500 Error after around 2 or 3 minutes.

I tried all forums on Opencart and tried to resolve the issue. i even cleared entire Cashe files in vqmod/vqmod.cashe; But problem did not end. I removed vqmod and reinstalled it. Still the error remains same.

I have to use vqmod for an extension smartimportexport tool. This problem is happening even before I bought smartimportexport extension. Therefore I do not think, this extension is the cause for this Error.

I use Kuler Theme on my website. I contacted them and they also suggested to contact a web developer who can resolve this issue as this is not happening due to their theme. I also tried default theme to check if the problem still there. It was there. Now I came to this forum to get the help. I have around 2500 products on my website and need to upload around 5000 more in next few days therefore I need immediate help.

Error:
2014-05-08 1:03:52 - PHP Notice: Error: Table 'being034_maindb.oc_product_to_category' doesn't exist<br />Error No: 1146<br />SELECT p.product_id, (SELECT AVG(rating) AS total FROM oc_review r1 WHERE r1.product_id = p.product_id AND r1.status = '1' GROUP BY r1.product_id) AS rating, (SELECT price FROM oc_product_discount pd2 WHERE pd2.product_id = p.product_id AND pd2.customer_group_id = '1' AND pd2.quantity = '1' AND ((pd2.date_start = '0000-00-00' OR pd2.date_start < NOW()) AND (pd2.date_end = '0000-00-00' OR pd2.date_end > NOW())) ORDER BY pd2.priority ASC, pd2.price ASC LIMIT 1) AS discount, (SELECT price FROM oc_product_special ps WHERE ps.product_id = p.product_id AND ps.customer_group_id = '1' AND ((ps.date_start = '0000-00-00' OR ps.date_start < NOW()) AND (ps.date_end = '0000-00-00' OR ps.date_end > NOW())) ORDER BY ps.priority ASC, ps.price ASC LIMIT 1) AS special FROM oc_product_to_category p2c LEFT JOIN oc_product p ON (p2c.product_id = p.product_id) LEFT JOIN oc_product_description pd ON (p.product_id = pd.product_id) LEFT JOIN oc_product_to_store p2s ON (p.product_id = p2s.product_id) WHERE pd.language_id = '1' AND p.status = '1' AND p.date_available <= NOW() AND p2s.store_id = '0' AND p2c.category_id = '245' GROUP BY p.product_id ORDER BY p.sort_order ASC, LCASE(pd.name) ASC LIMIT 0,8 in /home/being034/public_html/system/database/mysql.php on line 50
2014-05-08 1:03:52 - PHP Notice: Error: Table 'being034_maindb.oc_customer_online' doesn't exist<br />Error No: 1146<br />DELETE FROM `oc_customer_online` WHERE (UNIX_TIMESTAMP(`date_added`) + 3600) < UNIX_TIMESTAMP(NOW()) in /home/being034/public_html/system/database/mysql.php on line 50
2014-05-08 1:03:52 - PHP Notice: Error: Table 'being034_maindb.oc_url_alias' doesn't exist<br />Error No: 1146<br />SELECT * FROM oc_url_alias WHERE keyword = '500.shtml' in /home/being034/public_html/system/database/mysql.php on line 50
2014-05-08 1:04:24 - PHP Notice: Error: Table 'being034_maindb.oc_weight_class_description' doesn't exist<br />Error No: 1146<br />SELECT * FROM oc_weight_class wc LEFT JOIN oc_weight_class_description wcd ON (wc.weight_class_id = wcd.weight_class_id) WHERE wcd.language_id = '1' in /home/being034/public_html/system/database/mysql.php on line 50

If any of you have any idea please suggest. I have checked all tables in sql data. entire DB files are correct but error shows some of the tables are missing. I am not able to understand why this error is happening.